And not just that...

I'd mention ukraine, but even in peace time, there can be huge power outages in relatively large areas (as in US, more than one in the recent years), where point of sale terminals stop working, there is no internet connection to process the transaction, but exchanging a few bills, for whatever you need always works, even in the dark.

Also privacy... Want to buy a huge buttplug from a "Huge buttplug store ltd.", but your government could collapse in a few years and the new one might not like people (especially guys) using huge buttplugs? With cash, there's nothing to trace... with cards, the government can get a list of names in few seconds.