Is it customary to leave cartridges at war memorials?
There are cartridges and what appear to be challenge coins.
I leave a PBR, pack of Marlboro Reds, & book of matches when I visit memorials. When I checked with NPS, they stated they had several sets of such that were collected from The Wall. (They collect and save everything that is left there - even floral displays although most of those get photographed and cataloged.)
stay safe.