Amazonia is the rainforest region in the south of Colombia.
Most of the Colombian Amazon (including Leticia!) is so remote and isolated that food will have to be local, and thus having fewer and more expensive vegetables, less meat, and far less dairy. On the upside, this means that you will be eating lots of fresh food, like fish and fruit, and on the downside, you might wind up eating a certain amount of canned food as well. For fish, look out for local favorites like pirarucú and dorado. The former is leaner but delicious and the latter very fatty and rich. Piranha is another common local food, since the Amazon is really full of them. While too small to make for an easy meal, piranha meat is actually quite tasty.
It's hard as hell to find (it's a little more common in the Peruvian Amazon), but drink afficionados really should seek out chuchuhuasa, a spirit made from the bark of the eponymous plant mixed with aguardiente. Tasting much like a sweeter version of bourbon, the drink is more popular with locals inside the jungle, rather than in the towns, where it is generally not commercially available. It's actually pretty great for a jungle trek, as the plant contains a strong stimulant (and, reputedly, aphrodisiac) effect, in addition to conditional medicinal benefits, treating ailments such as diarrhoea, arthritis, menstrual irregularities, and upset stomach.
Yagé (pronounced yah-HEY, with a very soft h) is a drink, known better in other countries as ayahuasca, uniting virtually all the multitudinous and disparate indigenous cultures of Amazonia. A strong hallucinogen, its primary use is religious, for divination and healing. As it is potentially harmful, it should only be drank under the guidance of a shaman, who will both monitor your health, help you "see" more, and chant in the dark for hours on end. On the first use, yagé is likely to induce pretty serious vomiting and diarrhoea. If you are very interested in the drink, culture, and tradition it may be worthwhile to schedule two nights in a row with a shaman, which will really boost your chances of experiencing something more interesting.
You might assume that the remote jungle lands of Colombia might be the refuge of the FARC, but the fact is that much of it is too remote for even guerillas to operate. The extreme south is very safe (aside from natural dangers like snakes and mosquitos!), and visitors should not worry about violence on a trip to Leticia and the Amacayacu National Park. Western Putumayo, however (the extreme west of the region), is a hotbed of guerilla activity.