Great question — answering as the UphillTech team:
From my experience it is practically infeasible to carry food supplies for more than half a week and water supplies for more than a day. Unless you have porters or mules. Freeze-dried food can furthermore reduce the weight you have to carry. There are a lot of people walking the Way of st. James which takes about one month. The best prepared have less than 5kg backpacks. Everything around 10kg or more is going to spoil your walk. All you carry is a small sleeping bag (100-300g in summer), one change of clothes, flip-flops, toothbrush, raincoat, snack for one day and water. Everything else you either do not need or buy on the way. You can find a lot of gear left somewhere on the way :)
Full answer by crenate: https://travel.stackexchange.com/a/7111 (CC BY-SA 3.0).
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