I found two 'protective cases' with 6 slots, the yellow thing. I put food items into one and medicine items into the other. Put case 1 onto hotkey '9', and case 2 onto hotkey '0'. Pressing either hotkey causes the game to display the contents from case 2 only. The hotkeys also show the labels as case 2 and case 2. If I have another item (which is not a case) in my hand and drag either case 1 or case 2 into my hand they open properly (showing the different inventories). If I have either of the cases in my hand and drag the other into my hand it does not open properly- game will still display the current case's contents.