I am actually so confused. Shouldn’t they just carry a gun and ammo and maybe some rations?
The weight (an average) soldier carries has increased from World War I. If you look at the respective article for the equipment of a World War I soldier, you can ask yourself which items you consider dispensable.
This article probably gives what an average British soldier carried in World War I:
Over the centuries, the equipment has looked like this (there is also World War I British equipment displayed):
Today's problems with overweight:
And what the Romans carried:
The solution for the modern problems seem to be along these lines: