ETA: My picks are 3 & 4.

1. Open a new checking account with a debit card

2. The account is always at a $0.01 balance

3. Keep this card in its own specific pocket

Now anytime you go to buy something, the exact amount will be deposited into the account and immediately withdrawn for said purchase.

Congratulations, literally everything costs a single penny.

Implement the selling of items, the transfers to alternate accounts, etc., and you can create infinite money.