I like the idea of spoils of war a simple system could look like this imho:
- Part of the equipment of the losing side is salvagable after a battle
- You can pick it up with your army and equip your troops with it (if troop equipment change is possible after troop creation)
- Everything not used stays at that tile until a caravan (automatically generated from the nearest possible location) comes to pick it up (If units have inventories to store stuff, you could pick it up too of course)
- Loot vanishes after some turns and if not guarded(bandits are everywhere after all)
Personally I see no problem with loot staying on the map for some time. A bag graphic which when clicked upon shows it's contents would be enough to have.
A more simplified system when unit reequiping isn't possible and they don't have inventory space to store stuff:
- Part of the equipment of the losing side is salvagable after a battle
- You can chose if you want to keep the loot
- If yes, an automatically generated caravan brings it back to the nearest city
- If no the lood gets deleted (salvaged and stolen by the nearby populace, monsters, robbers, whatever, not game effect just flavour text)
Such a system doesn't need to be very complicated after all, just be something to reward one with something for winning a battle. (Also it could make my carreer as a robber baron possible. Instead of producing weapons, I'll just steal them from my neighbours.
)