Would be interesting. Maybe a little card similar to a prepaid TracFone phone card, with the public key and private key under a scratch off area, but these cards would have to be put up in a display case with a lock, to prevent people from just scratching them off in store and stealing the money since normal prepaid cards get activated on check out, so they are useless till checkout but Bitcoin would have no clue if the card was checked out or not. So you would only have the cashier give you the card at checkout, like how stores keep cigarettes locked up behind glass.
This is really not an issue seeing as you could send the bitcoins to the card at the checkout (so the cards on the shelf have a 0 balance until you scan them and X bitcoins get sent to the card address)
This is also great for preventing major thefts. For example a store could have millions of dollars worth of bitcoin cash/cards onsite, without actually have a single dollars worth of bitcoins onsite. The actual digital bitcoins could be controlled by someone at a remote location, so even if the robbers demanded the cashier load up the cash cards, they wouldn't be able to.
