Guess what you can’t do when the power goes out for a few days? Buy anything. Cash, check or charge. Try buying gas when the power is out. Try getting bread when the power is out.
Then they use generators that take debit and batch the information until the power comes back on.
I have never had difficulty buying anything with cash during a extended power outage. As long as I had anywhere close to the correct amount of cash, the sale was completed.