If I needed cash, I'd raid my kids' little stashes. They probably have about $100 total at any given time. We deposit cash into their accounts from time to time though, so that well could be dry. When the wife and I were serving, we'd have anywhere from several hundred to a few thousand dollars on hand because we didn't ever deposit cash tips. It's easier to just bring some with you and spend it than it is to deposit it and then spend it.
I like the subject though. Out here, water is more valuable than cash in the summer. If there was an outage, I'd rather be sweating, temporarily broke, but with plenty to drink.