The "national drink" of Peru, at least as claimed in the tour books, is the Pisco Sour. Pisco is similar to brandy in that it's a liquor distilled from grapes, but it's less sweet. The sour part involves Peruvian lemons and egg whites, among other things. I must admit I wasn't a big fan of Pisco or the Pisco Sour.
The Peruvian lemons are pretty good without the egg whites though. They're small, green and intense, not far off from the limes we get in America. They also make fantastic lemonade. I ordered it several times, and it was consistently a treat. I think it was made fresh every time I ordered it. It looks pretty tasty too -- I'm disappointed that I didn't get a photo of it.
Fruit juices are more widely available in Peru than in the US. Most menus had strawberry juice, papaya juice, and others. Wendy's favorite was strawberry juice. As served there it's a thick, sweet beverage almost like a milkshake. But since it wasn't called a milkshake we can pretend it was healthy.