Silpancho
Or milanesa - beef pounded to a thin, plate-sized patty, served on a bed of rice and potatoes, with a fried egg on top similar to wiener schnitzel.
Coca leaves
Coca has been part of Andean culture for centuries, and chewing is still very common and perfectly legal in Bolivia. You should be able to buy a big bag of dried leaves at the local market. Coca is a stimulant, and it also suppresses hunger. Chewing a wad of leaves for a few minutes should bring slight numbness to your lips and throat. Remember the slogan printed on souvenir T-shirts: Coca no es Cocaina "The coca leaf is not cocaine". But cocaine most definitely is an illegal drug. Remember this, only chew the leaf; if you eat the coca leaf you will get a very sick stomach.
The cuisine of Bolivia might be called the original "meat and potatoes" -- the latter locally called papas from the Quechua were first cultivated by the Inca before spreading throughout the world. The most common meat is beef, though chicken and llama are also easily found. Pork is relatively common. Deep frying chicharron is a common method of cooking all sorts of meat, and fried chicken is a very popular quick dish; at times the smell permeates the streets of Bolivian cities. Guinea pigs cuy and rabbits conejo are eaten in rural areas, though you can sometimes find them in urban restaurants as well. A common condiment served with Bolivian meals is llajhua, a spicy sauce similar to Mexican salsa.
Some notable Bolivian dishes:
Pique a lo macho
Grilled chunks of meat in a slightly spicy sauce with tomatoes and onion, on potatoes