I keep a few grand in small bills stashed around the house. It's one of those things you just might be ridiculously glad you have in the unlikely event you need it. Imagine a natural disaster or a ten day blackout.
I'd like to know how to survive for a week without my debit card, then. It's my only really consistent source of money.
Or imagine the FBI freezing your bank accounts. If there's a 10 day blackout, odds are you're not going to able to buy much, anyway; ditto for natural disasters - and you can usually drive far enough away to get money from a place with power. If your assets are locked, you're screwed no matter where you go.