How to Pack for 4 Week Trek? [closed]

The two constraints you have are load and variety of climate. Normally any trip longer than 10 days or so requires the same amount of clothes and you will have to plan to do laundry at regular intervals. In an 80L backpack, I seem to be able to fit clothes for 10 days, maybe less for colder weather, more for warmer place. Although my female friends seem to manage at least 50% more given that their clothes are smaller and lighter.

Between Iquitos and Torres del Paine, you will encounter the greatest difference in temperature, with the Inca Trail falling somewhere in between, depending on your luck with the weather. In any case you need to have clothes for a hot and humid place, as well as cooler weather.

Therefore what you need is 8 days or so of light easy-to-wash clothes. When you encounter a laundry facility, it is best if none of the items require special care. Cotton is cool, breathable and easy to take care of. Some people swear by synthetic fibers which are easier to dry but I've really found some that worked for me.

Add to that items which you can layer, making sure to have at least a light and medium weight waterproof outer layer and warming intermediate layer. In some places, you will end up wearing 3 layers at a time, others just one but that makes it possible for you to adjust as you move between climates. This is good use of performance fabrics which give good thermal isolation for low weight.

Short hiking boots and shoes are essential, plus underwear, socks and a bathing suit. There are lots of places where cooling off in the water is possible in the jungle. Your guide will be able to point out the ones which are safe and the ones which aren't.

When I did the Inca trek (over 10 years ago) these are the things I wished I'd had:

1 - Trekking shoes with a great grip - mine were slightly old and the grip wasn't great. It made going down steep steps really hard.

2 - Quick drying trekking gear for the sudden showers

3 - A nail clipper. If you have to trek down high steps toe nails can start hitting the front of your boots and get really painful.