The quick-draw / carrying harness

An arrangement of straps worn over the body and rigged so that two more pieces of kit ride where a hand can find them without looking. Either comes free in the middle of doing something else, which is the difference between a flask that is in the pack and a flask that is in the hand.

It carries better than a pack as well. The weight sits where a body can take it, and a man wearing one hauls as though he were a little stronger than he is.