Step3
Go to the grocery store with cash only.
If you just need to pick up a couple of items, take a $20 bill.
If you're going to do a bigger shopping, take $60 the first time you do this, or give yourself a budgeted amount.
Look at the price of every single thing you purchase, and keep in mind that if you go over your cash limit, you'll be redfaced at the register.
This doesn't mean changing the basic way you eat, doing without your favorite things or buying in bulk. It just means being conscious of the cost of every single purchase and aware that our purchasing power (for that particular trip) isn't infinite.
If you've had the experience of "just running in to pick up a box of cereal" and winding up spending over $50, you will probably be thrilled the first time you go into the store with a $20 bill, and come out with a box of cereal and $17.39.
In short, you set your one-time budget by only having cash, and you see what you saved, because it's real money.