What is The things they carry?

Everything they carry is precious in some way--it has to be, or they wouldn't carry it, because many of them already carry at least twenty pounds worth of gear. What they carry is decided by their fear (some of them carry more ammunition than others) and by their homesickness or desperate need for distraction from the war (Rat Kiley carries comic books, and Jimmy Cross carries pictures of Martha). Some of them carry good luck charms. They all seem to know the weight of each thing they carry, because each thing is a necessary part of them, for one reason or another