With the new 1.04 update, I've found an assault bag, an assault pack, an assault vest, and a ballistic vest. So they can be put into inventory empty. When in hand, they can not have items loaded into them. You can place items into them when they are placed on the ground, however can not be placed into inventory with items inside, the packs, bags, etc can only be taken into hand. Having found good loot early into the release, I'm hoping to not part with the items due to bugs, although I've already had to part with a nice black assault bag.