Be on the lookout for errors
Watch prices at the register and check your receipt before you leave the store. Grocery stores change thousands of prices on items each week, Nelson says. "That means there are thousands of opportunities for pricing errors. Some stores will give you an item free if you are overcharged, but it's up to you to point it out," she says.
And don't forget to utilize the most old-fashioned strategies: Stick to your grocery list and shop as quickly as possible so as not to add unneeded items to your cart. "The longer you hang around, the more likely you are to veer from your list and spend more than you'd planned to. Get in and get out," Nelson says.