Shiny Credit Cards are very nice. I wish I had any that worked. Fact is, though, you can’t exactly grease the wheels with a bouncer or tip a bell boy with plastic. When the apocalypse comes, trust me, the people with no foresight will think cash still has value and you can trick those suckers with the green.
Seriously, though, even if you use a credit card, you can and should still tip in cash, as 
most bartenders/waiters/waitresses have to pay a processing fee (at the very least) on their credit card tips.
Also, I feel like it goes into the same vein as (#49) Emergency Preparedness. You never know when you’ll need cash, and there may not be time for ‘let me just stop at an ATM.’ Have the money on you, and you can buy that homeless guy’s awesome shoes or some painting you see some street artist doing, or something that doesn’t involve purchasing something on the street.
And, when discretion is the better part of valor, and the guy mugging you has a gun, he won’t be satisfied with no cash, and might TAKE YOU on an ATM run, you’ll think back to that moment where you left all those bills on your nightstand, and realize you could already be out of this situation.
I’m sure there are many, many more reasons to carry cash, but you’re big boys, you’ll figure them out in time.
The Step- Carry cash at all times.
Have I Done It- Always.
The 10,000 Steps to Becoming a Man. 