Light clothes (shorts, T-shirts, better too large :-) made of natural materials (cotton) for warm/hot days all year round.
Sweater/pullover and/or jacket for cold evenings/nights (from November till April).
Shoes? Oh, yes - you should have them :-). Sandals for walking and/or good walking shoes for trails around (dangerous reptiles and insects possible).
Add sun glasses.
Check the 10-day forecast for Yuma (46 miles = 74 km west of Tacna):
National Weather Service
Check the average weather conditions in Tacna in 1970 - 2000:U.S. Weather Station in Tacna
Good sun protection cosmetics with high UV filter - use them BEFORE or just after you leave your car.
Be prepared for large contrasts between sun and shadow - sun filters recommended. Add hmm... how do you call it in English - something fixed to your camera objective to protect it against sun - not comfortable to carry but necessary, I suppose.
Tourist frige with ice cubes and cold beverages inside :-).









