I have followed several long distance walkers, one on a blog and an other in the book they published about it, as well as seeing blog items that I do not follow long term.
They use wheeled transports, dragged behind them, for those parts of their trip when they needed to transport more than they could carry or even for the whole.
Here is a link to the blog I followed. Only a small part is in English, but it is enough to show what he used. Jan Vroomans walked from the Netherlands, with no destination in mind, towards the east and decided it was enough when he was in China. Early on, maybe even from the start, he used a two wheeled luggage, at this time I can not find it on internet, the nearest I can find is a āBurley travoy urban bike trailerā, which might do the job.
One of the others used a more conventional hand kart which he dragged behind him, gripping it with one hand. And he only used one for the areas where re-supply would be very hard, like in the USA deserts.
I would say, having done it, that a 15 kg backpack is within reason for carrying, if on the heavy side when untrained. People I met traveling were carrying 30 kg backpacks, without training and out of an office job, they did suffer from back and knee complaints a few days in.
When you are trained up you can carry more than 15 kg for a few days, specially if you are not overweight, overweight people carry more than that extra over their proper weight all the time and their bodies do adjust to it.
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 š
Credit:stackoverflow.comā