the other sugestion is, sorry if i didn't explain it correctly, that:
when you are moving through the map, you are traveling, so all the inventory have to being carried by your men/horses/supply wagons
the idea is give to all that "transport" a presence in the battlefield when you are atacked (you don't have iniciative so you have to engage without being prepared, so you can't leave the cargo in a secure place before battle (the cagro you are carrying must be present in the battle in the form of:
transport wagon if you have one, or a bunch of bags and inventory that soldiers drop in the place before battle (instead of the normal trunk)
when you are attacking, you have the initiative, so it is supposed that you have leave your inventory/cargo/wagon, out of enemy sight, so adding the wagon or cargo to the battle it is not necessary.
this will give a better logic conection between the map and the field of battle, enhancing inmersion and realism, almost in a aestethic way.
sorry i can't explain it better in english, if it is not clear enough i will send you a PM en español