[Clipper]

It is unclear what you mean by backpack. Could you please elaborate as to what you mean by playing cards into your backpack?

If you mean a set of cards that you are not currently using, such as a second piece of Headgear, then you indicate those by turning them sideways, and that is described in the rules. The correct way to refer to these sideways Items is those not in use or unequipped. You may also see the term carrying, which refers to all the Items you have on the table, whether equipped or not. You lose all those Items when you die and it does not matter if they were equipped or not at the time.