Normally, you can only carry 50 kliograms of weight, which pretty much you can lug around several hundred rounds of ammunition, the weapons that fire the ammo, armor, grenades, etc.

However, you should notice you can load all of those items on a human dead body (not animals or mutants), and simply use the SHIFT + USE function to drag the corpse along with you. This way, you can load a corpse with any number of items and move them from one location to another.

Since you cannot attack while dragging a corpse, you may only want to use this "one slow trip" when in a situation that has left very few enemies on the map.

Additionally, you cannot take a dead body from one place to another (meaning all this must take place on the same map). Items on dead bodies also randomize once you switch maps, so never leave items you want to keep on a dead body, or you lose them forever when you go to another place.