It is instructive to explore souvenir shops. The souvenirs I have in mind are not those items that can be found everywhere and that have no genuine link to a particular place; things that are made in bulk and simply adapted slightly to fit the location in which they are being sold. The souvenirs that nobody you know would ever really buy, but they do, of course, sell: the little plastic televisions with a number of popular images to click through, all-black postcards of a city at night, dolls in costume, T-shirts with local images that you last saw worn at the airport. The more up-to-date range includes postcards that allow you to rebuild famous monuments, bottle openers in the shape of certain sights, regional versions of Monopoly or notebooks with town plans and index stickers - the last a nod towards the contemporary city dweller who has fallen in love with a metropolis. Souvenirs are a major industry and an important aspect of popular culture. After all, even the philosopher Walter Benjamin appreciated snow globes.

The history of souvenirs is characterised by the wish to remember, for better or worse, using an object to make an experience more "real", turning something initially meaningless into something meaningful. It can be traced far into the past - at least as far back as the Crusaders, who took home small-scale replicas of the Holy Sepulchre; modern-day tourists replace such architectural mementoes with equally symbolic inscribed slices of olive trees. The importance of pilgrims as providers of business opportunities is documented as long ago as the 13th century, when they were sold small tin badges on the road to Santiago de Compostela; today's range is wider but still an important part of the overall experience.

The list of souvenir-seekers is easily extended: explorers, emigrants, 18th-century aristocrats on their Grand Tours, prisoners and, of course, throughout the 20th century, tourists keen on mementoes for fun, enlightenment or the triggers of personal memories that make keepsakes not only interesting but, at times, magical. Souvenirs can even turn into a statement of loyalty and association or a sense of participation in specific moments in history - whether linked to the death of somebody famous (John Lennon, Diana, Princess of Wales or Michael Jackson), a place in crisis (New York in 2001), or a sense of taking part in history in action (the fall of the Berlin Wall in 1989). The limited-edition series of miniature Buildings of Disaster that the artist Constantin Boym created from 1998 onwards - including the reactor at Chernobyl, the World Trade Center and the Alma tunnel in Paris - takes this just one artistic step further.

In recent years, the traditional souvenir shop has met competition: in an age that does not shy away from the miniature-format "book snacks" and "books to go", some bookshops now offer considerably more than just books. Museums, too, have moved a long way from a selection confined more or less exclusively to postcards; today, wares displayed in their shops can at times appear to offer serious competition to the actual exhibitions. The added value that was born of 1990s "event culture", the boom in all things related to memories and the steady growth of tourism thanks to low-budget airlines, is reflected in a new and often original range of goods - most of them also available from museum websites boasting sections highlighting "top sellers" and "special offers".

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"Top sellers" may well tell us something about contemporary issues, and most certainly about topical issues - unless the popularity of reprints of the Ministry of Information's 1943 booklets Make Do and Mend and Wise Eating in War Time, both available from the Imperial War Museum shop, is purely accidental in the midst of the credit crunch and kitchen-garden revivals.

Then there are the imitations and reproductions of beautiful exhibits - frustratingly untouchable as the real items on formal display, but now available to take home as cultural history in miniature form. Paintings are particularly versatile - having been broken down into jigsaw puzzles, or used to adorn a shopping bag or notepad, they are removed from exclusivity and the realm of aesthetics and belong to trend and commerce. Other items can be looked at in practical terms: pasta available in the shape of a city's icon or logo, or assorted chocolates with various images (say, Henry VIII's wives with him in the middle). Wine can also be sourced from unconventional places: the Karl Marx museum in Trier, Germany, offers bottles from a vineyard that belonged to Marx's family. What all these examples have in common is that this kind of "visitors' digest" (as academic Harald Kimpel puts it) loses the connection with the place, person or time in question; the marketed object takes pride of place over the original.

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Scholars, including Pierre Nora, Andreas Huyssen and Jan and Aleida Assmann, to name but a few, have highlighted the importance of memory, be it in the form of memorials or retro-culture. Souvenirs, in particular those that in one way or another reflect history, represent the ever-changing meanings of the past in the present. They are indicators of what in popular terms is the "essence" of past times - cultural memory as a mixture of general perceptions and market forces.

Questions arise when political history comes into play: what do playful items that depict, for example, once-important images representing a country reveal about our perceptions of history? And what does it take to turn serious issues into memorabilia, some of which blatantly make fun of tragic events and people? Human-rights campaigners have highlighted the existence of "Greetings from Guantanamo Bay" postcards that are a sign of a flourishing holiday business and betray a shocking lack of respect and decency. Or, moving back in time, the late medieval and early modern Western and Central European witch-hunts cost, by some estimates, 50,000 lives, most of the victims being burnt or drowned, more often than not after extensive torture. One of the most infamous examples is the Salem witch trials in New England - notorious not least because they took place in 1692 and therefore encroach uncomfortably on our wishful perceptions of the continuous enlightenment of mankind. Twenty "witches" were sentenced to death. Irritatingly, the Salem Witch Museum stocks in its shop - the culminating and unavoidable final point of a visit - items such as the "Witch City chowder mug" and the "Salem skull T-shirt". Even terror, torture and death, not just the (in)famous dead, sell.

The question is no less problematic when, with the passage of time, the real meaning of images is first forgotten and then lost. Ian Hawkins' 2008 documentary My DDR-T-Shirt supplies fascinating answers to the impact of some of these "decontextualised" souvenirs. The film was inspired by a trip to Berlin where Hawkins bought a DDR T-shirt - one of those shirts emblazoned with the German Democratic Republic logo and available on the internet, in souvenir shops and from the street vendors who also offer more (and at times less) authentic souvenirs of the former Soviet Army, including curiously out-of-place Russian military hats and gas masks.

Hawkins took the "pangs of conscience" he suffered after buying the T-shirt as a starting point from which to explore what these symbols really meant to people who had experienced the regime between 1949 and 1990. They include visitors from the West and residents who grew up with the socialist dream: in one instance, a British communist who embraced the system; the widow of the founder of the Checkpoint Charlie Museum; and a former prisoner who had tried to smuggle his girlfriend into the West. Predictably, not one of them would wear such a T-shirt. Some would take issue if they saw someone wearing it, while others would dismiss it for what it is: touristy kitsch a far cry from the realities of life in the German Democratic Republic, as Hawkins powerfully explores. What is striking is the intense emotions such a T-shirt can trigger, confirming that history and its reproductions are always just one version of the past. In the case of the DDR T-shirt, it is the rather thoughtless representation of history that not long ago was reality. After all, the state in question existed until 1990.

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The reduction of actual history into tangible chunks is a rapid process, and what remains is mostly taken out of context. When designer cookies became available in the form of Berlin's best-known sights, it did not take long for a bar of chocolate to challenge the prospective customer "to let the Wall melt on your tongue". At what point did the Wall, the division between East and West, become so funny? Twenty years on, if one were to trust souvenir shops, the former GDR can be summed up by its notorious cars (the Trabi, available in all sorts of miniature formats), the Ampelmannchen (the rather didactic-looking traffic-light signs available as ice cube trays, towels, sponges and cookie cutters), plastic crockery (with an obvious bias towards egg-cups) and, of course, the Wall - bottled in one version, with a choice of blue or gold writing, reduced to inserts on postcards and reproduced in miniature sculptures.

And now there is a new generation of souvenirs, commemorating the 20th anniversary of the fall of the Wall, giving the whole affair the promotional value of Olympic Games marketing: the past can always be topped by its anniversaries. Just like film-makers and writers, the designers of these objects contribute to the continuous reinventing of the past by the very choice they make, the very spin they give things. But with the "typical" products comes a certain attitude, in which history is reduced to the cliches of mass-produced goods far removed from the complexities of reality. And, in Richard Terdiman's term, they are in fact "present pasts" in that the link with whatever really happened before is broken for good and new narratives are established.

The contemporary obsession with "real lives" - daily life and its objects - has impacted upon exhibitions and museums, which in turn offer souvenirs that develop a strange dynamic out of context. The more complex issues are hidden away in the book, map and film section. The weird and wonderful goods that now serve to represent the German Democratic Republic underline what John Lewis Gaddis takes as a starting point in his book, The Cold War: A New History (Penguin, 2007). He describes the attitude of his students, coloured by hindsight: "What could anyone ever have had to fear, they wonder, from a state that turned out to be as weak, as bumbling, and as temporary as the Soviet Union? But they also ask themselves and me: 'how did we ever make it out of the Cold War alive'?" If you take a walk around the souvenir shops and survey the wares of street vendors in Berlin or other Eastern European cities, these questions may seem to be confirmed by the plastic cars and the abundance of gas masks.

But perhaps the case is even more startling when one considers the life and afterlife of Ernesto "Che" Guevara. The Argentinian medical doctor - a Marxist, a key figure of the Cuban Revolution, the author of influential books, and a fierce opponent of modern consumer culture - was executed in Bolivia on 9 October 1967 at the age of 39 and has since been named as one of the 100 most influential people in the 20th century. Alberto Korda's famous and readily recognisable photograph of the "Guerrillero Heroico" has played its own part in the merchandising of the revolutionary. Out of context, out of location, out of time, the collective imagination has created its own image of Che Guevara as a global phenomenon. In terms of souvenirs, this includes the now-familiar range of mugs, bizarre T-shirts for dogs and a "No Che Euro-Style Oval Sticker" for the car.

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In 2005, the School of Visual Arts in New York mounted an exhibition called "Souvenir ... The Rest Is History". The title is fitting. It is fascinating to consider the displays in any souvenir or museum shop - what is on these shelves that contributes to summing up, say, Winston Churchill? The answer would include vintage kitchen and garden tools, D-Day playing cards and a "Camo[uflage] Squeezy Teddy". What sells now says something about our shared personal and popular preferences. But it also affords interesting insights into contemporary popular narratives - and how the next big event may also be turned into instant "souvenir history".