I had a Plate Carrier armour piece. I had found, and attached, its pouches. In its pouches I had binoculars, and a yellow storage crate (itself containing a PET and a cooking pot). I then found an attachable holster. I attached the holster, and the inventory of the pouches was nix'ed - I lost my binoculars, PET, pot, & crate. My binoculars were on my hotkeys, but after attaching the holster to the already-full and pouch-laden Plate Carrier, my binoculars disappeared from the hotkey menu.