Keep your card in view after you give it to a clerk. Watch your credit card slip being filled out - and make sure it's not passed through the machine more than once. Ask for your carbons. Destroy the carbons, but keep your credit card receipts and check them against monthly bills. Destroy carbons before throwing them in the trash.
People go through the trash looking for credit card receipts to obtain the number to make purchases.
When your monthly statement comes in you notice several purchases that you did not make. Destroy every credit card that's out of date. Cut it in half. Throw it away. Get rid of it.