Carrying Around an Expensively Empty Wallet
I know, I know, you're so used to paying for everything with plastic that you rarely bother with greenbacks. But having some cash around never hurt anyone. You know what hurts? Buying four extra brownies so you can still get your $2 coffee at the café that has a $12 credit minimum. Or even worse: leaving your groceries in the checkout line so you can trot off to find an ATM when the credit card machine isn't working.