I don’t know about Samsung and Apple, but Google Pay works offline.

I haven’t tried it yet, but I’m wondering if it would be possible to buy a Google Pay compatible virtual debit prepaid card with monero, like $50-$100 and use a card writer to put it on a plastic card to use in store. Then just buy another one after its depleted and rewrite the card with new details, rinse and repeat. That seems like the closest thing to digital cash you can get without xmr being accepted by merchants.