In The Things They Carried, Tim O'Brien uses the cataloguing of things to show the dualities between the physical and the emotional, the concrete and the abstract, peacetime and wartime, and the lightness and heaviness of things.
In general, the men carry according to their size, rank, and role. In terms of organization, the description of items moves from light to heavy things. O'Brien includes the physical weight of things to juxtapose those abstract things that cannot be weighed, namely fear.
All the men carry fear: the waiting is the worst.
All the men carry ghosts. Ted Lavender is introduced as a ghost, and Cross carries his dead body literally (after he is shot) and figuratively (guilt).
All the men carry love. Cross carries Martha's picture and letters. He says he burns them. Later, he says he kept them. Does it matter? Like his love for her, which may or may not be real, the things these men carry burden them down by sheer volume, even if they don't really exist.
Besides the basic tools of warfare each soldier carried, they also carried mementos of home - photos, letters, scraps of cloth or handkerchiefs - anything that symbolized to them what they were either fighting for or fighting to return to. Playing cards for boredom, symbols of protest about the insanity of war or their mission there.
And each soldier carried, as in every war, the stresses and strains of combat, the PTSD associated with prolonged exposure to danger and death, the memories of fellow soldiers who were killed or wounded, and every other burden typically associated with war.
What O'Brien does so well is to combine all of these things, physical and emotional, into a single theme that flows throughout the entire set of stories. It allows the reader to understand and think about all of these concepts and ideas related to those burdens, even though they likely have never been in combat and never will be.