During natural occurring regional disasters credit / debit and money in checking / bank accounts regardless how much / line of credit is, is typically inaccessible therefore pretty much worthless but cash in hand rules. During a widespread power outage that lasted multiple weeks for many due to a severe ice storm several years back I watched people wanting to buy gasoline / diesel, LP, kerosene, groceries, medicine, etc., etc., get turned down time after time because businesses AND banks / credit unions couldn't process electronic transactions.
As an added suggestion -- also wise to keep some cash in small denominations or else accept the probability of not getting some or any change back.
