1. For a largish purchase, go to the bank, withdraw cash to make the payment.

First, the bank will cross-examine you as to why you want so much cash. It's none of their business but they will prod you.

Second, when you see how much money five thousand dollars are, it makes it harder and least for me to spend.

2. If I put cash in my wallet, and the denominations are 100s or 50s, I am reluctant to spend them. If they are twentys or smaller, they seem to disappear fast, because they don't seem so big.