So the taco place was open..but their credit/ debit card machine was down. Emergency $20 bill to the rescue. The tacos tasted even better...Knowing my EDC saved the day

Yes! Always carry cash, and have an emergency stash at home. Amounts will vary with circumstances and needs, but never be without.

Cash is by far the most flexible and often-used item from my EDC.

One of the EMP based disaster movies reference here showed a dad trying to get money out of an ATM to be able to buy supplies for his family.
No dice.
I've started carrying enough cash to get a room and meals for at least a day at all times.
Having had my identity stolen, perhaps with the aid of credit card copied at a business, I've also started paying with cash for as much as possible unless I swipe the credit card myself.

I usually carry $60. I should probably carry more. Except, that same $60 has been sitting in my wallet for years. Guess I don't run into too many emergencies.

I use cash much more than plastic -- gas, food, sundry items. When I have less than $100 in my wallet it's time to stop by an ATM.

I've added a spare set of keys to my EDC along with twenty bucks

I always have an excess of cash. But that's not because I use it often. Instead, it's because I always use my credit card (paid in full every month, so no interest - it just accrues bonus points). However, all my friends want to use cash at lunches, so they pay that to me while I put everything on my credit card. So I end up having to clear the excess cash out of my wallet on occasion, just so I can fold the silly thing. I haven't had to withdraw cash from a bank or ATM for ... decades. I have no clue with my PIN is, of if my ATM card is still any good.

I go back and forth on if carrying change is necessary...

“I do not regard myself as a dead shot, but I am a pretty dangerous man with a wet towel. But all in all I think my favorite weapon is a twenty-dollar bill." Raymond Chandler