Why not use alcohol? Good for entertainment, hard(ish) to make, high in demand even now. And in a cataclysm scenario it can be A) safe to drink B) provide food (lots of kcal in booze) C) provide ‘entertainment’ D) Disinfects.
For more ingame usage, you could convert the creditcards to some sort of system that allows you to ‘link’ 2 cards to switch the debit values around on the cards. That way people could trade cash, and you could convert the barter system to creditcards once again. (And stop the selling of creditcards to npc’s exploit).
Or use a barter system and give bandages, medical supplies and other things (like water) sort of default values. And let the NPC’s talk about that stuff being in high demand. Food probably also has some value. Esp in high volumes.
(And there is of course barter, 2 normal people exchanging some small stuff, and large scale trade where you use your car/cart/dog sled, to supply settlements with rebar/food/guns/mutagen).
(I read an interesting story about the collapse of a real westernish country ages ago, and what the people there did to survive. (mostly business as usual, just everybody had guns, and you didn’t go out at night. And you never stopped for somebody while driving towards a safe place) I do recall it having some trade stories. But I cannot find the story anymore).
