The Basics
valid passport
(visas are not required to visit Perú as a tourist)
money belt for added security
Peruvian currency (U.S. dollars may be exchanged for Peruvian Soles at the Lima airport)

Clothing
warm jacket (you may prefer to purchase a nice alpaca jacket or sweater along the way)
layered clothing (sunny days will be warm, evenings cool or cold)
sun hat and/or wool cap (can be purchased in the Andes)
sturdy walking shoes suitable for steep, rocky terrain
sturdy sandals or light shoes for casual time
five pair of socks
rain poncho

Miscellaneous
personal day pack ~ lightweight towel
large ziplock plastic bags ~ wet wipe packs
2 one-liter water bottles ~ lightweight flashlight
camera/film or digital cards ~ ample batteries
 220v to 110v voltage converter
if you plan to charge electrical devices or batteries
(electrical source in Perú is 220 volt power)

personal toiletries
personal medications
high altitude prescription - optional*
*Note: maté de coca (coca tea) and/or chewed coca leaf are the traditional Andean remedies for altitude sickness.
 They work very well and are legal in Perú

We suggest you visit the website of the
International Society for Mountain Medicine
for useful information about altitude sickness
http://www.ismmed.org/np_altitude_tutorial.htm