Ok so let's say you have a Smersh Vest (8 slots) and you place two empty High Capacity Vests inside it. If I have something in my hands like a AK-74u (which fits a high cap perfectly) and I press X to remove it from my hands it will go Into one of the empty vests. So yeah it works with anything. I can have an empty jacket in my backpack and be totally out of inventory space and if I have a can of food in my hands then X remove it from hands it will go into the jacket instead of ground.