Heading across Arizona one time on the interstate we were in a near panic when 3 gas stations in a row could not process credit card transactions. Then the light came on. We actually had cash with us and the problem was solved. Felt pretty stupid being in a panic when we actually had quite a few dollars tucked away.
We now consider maybe a thousand bucks as a comfortable minimum. And it is puzzling how few people actually carry a lot of money with them. I can't think of a single time over a long life time when I ever lost a single dollar from any bad guys or stupidity or such.