I normally pre-equip my troops before leaving the base, then depending of the craft, scenario and such, I may or may not press CTRL+ALT+X to remove all unused items off the craft. In some cases I may add some small stash of ammo and med-kits using the "add on top" feature.
Wouldn't the player just stuff all the junk in the inventory, and then drop it before the battle?
I know it's limited, but still possible, and encouraging metagaming...
If you play like me, my soldiers are stuffed to the max weight possible with everything they
might need. Some outfits may be limited in space. So no actual room to carry stuff, except maybe for items in the other hand. My units would look like Arnold in the movie "Commando" at the beach scene :-)
But you raise a good question. How the requested feature would work when at the unit equipment screen before battle, items are dropped. In this case, I'd imagine it would work the same as in the multi-level scenarios where the troops advanced to the next level by rushing to the exit and not killing everyone. The loot pile made of discarded inventory items will be generated at the default location (position of first soldier).