1. Add a backpack or vest to a unit in the Virtual Arsenal
2. Observe the inventory on the right; the bar at the bottom will show items already inside, but you cannot see what those items are and cannot empty them out.

It might also make sense to simply be able to see everything inside the vest or backpack so that we can hit the minus button next to it to clear it out. It would be useful for there to also be an "Empty" button alongside that, however.