In O'Brien's novel The Things They Carried, the description of items in this first chapter, “The Things They Carried,” moves from concrete to abstract things. It begins with military necessities (guns, helmets, radios, ammo, rations) and personal items (comic books, pictures, letters, drugs) and ends with emotions, memories, family, history, tragedy, heartbreak, guilt, love. In this way "carry" is a transitive verb: it requires direct objects, and O'Brien lists them, and their weights, to give the novel military verisimilitude and to give the men psychological baggage.
The heaviest thing they carry, ironically, can't be weighed at all: the “unweighed fear.” Jimmy Cross, a Christ-figure (initials J.C.), carries the guilt over Lavender's death. His mind was on Martha, girl who symbolizes the comfort of home, when Lavender was killed.
After his death, Lavender's ghost hangs over the novel like King Hamlet's Ghost: “ . . . they all carried ghosts.” And “they carried all the emotional baggage of men who might die.”
In the end, to atone for the death (again the symbolic Christ-like metaphors), Lt. Cross burns Martha’s letters and photographs? (p. 23) Or so we think.