What is a consumer money-saving hack that anyone can do that few people know about?

Two options: 1) There are specialist money transfer cards that allow you to transfer your credit balance into your bank account for a small (1-4% usually) fee. You lose some profit but it's very easy. 2) Generate useful debt. I pay my car, house and health insurance, council tax, energy bills upfront and bulk buy non-perishable goods like toilet roll, toothpaste, soap etc along with any other big purchases. All of this goes on the card, leaving a lot of free money to save and reap interest on. Doing both at once generates max profits. Now you're not talking massive amounts (I'm clearing about £50 a month in interest at present) and you need to be disciplined, but any time you can get savings interest rates of 4% or higher, it's generally worthwhile.