The best protection is simply long sleeves and pants in light material and a full-brimmed hat. Suggest you buy sweaters when you get to Peru. Try traveling with just two pair of pants. Women may want to substitute pants with a comfortable skirt. The weather is cool, but bring a light pair of shorts if you wish.
Nights are cool to cold, sometimes a few degrees below freezing.
Many Andean buildings are not heated so you will need to dress warm as if camping. Long underwear and loose clothing for layering are advised. Be sure to have good traction soles if this is something you have become dependent upon. For easy cruise comfort, sneakers or sandals, which are the choice of most natives, are fine. If you have two changes of clothes, you wear one while the other gets cleaned.