If in doubt, instead of getting everything here, you could wait and buy some clothing in South America, as needed. I was surprised at how much of the same gear we have here, you can get there. I would, however, invest in the best shoes you can get here and be sure they fit perfectly. I even have difficulty finding a pair or shoes that fit me here!

You probably will not be able to predict every possible weather condition, but each locality should have clothing and supplies appropriate to that location's weather. Bring clothing for normal conditions; buy locally any extra items for those odd-ball infrequent conditions.

Some places have mosquitoes or fleas/flies that carry diseases, such as the infamous sand fleas of Machu Pichu. These fleas that hang out in grass attack ankles. As silly as it seems, I took gaiters. I also took my "bugs-off" clothing- pants, shirt, hat and a head net.

This has nothing to do with "layering" but be aware that water quality is questionable at best, so be sure to have a good system for water treatment. Chlorine tablets are small and light weight and I would consider them an essential. Everyone drinks bottled water, but you could get stuck in a place where you have to drink untreated water. You should be able to buy locally the water treatment chemicals needed to wash produce. You need to treat tap water you use to wash produce. Almost ALL tap water is bad. My husband and I both got sick and his pro-biotic tablets were really helpful. I also had some electrolyte replacement powder (Emergen-C makes packets of these).