You don’t make a grocery list.
It’s important to take note of all the things you need to buy before leaving the house. With a list, you're less likely to pick up items that you don't really need, or worse, you already have! Speaking of items you already have...
You don’t check your pantry before leaving.
Before heading out, check what’s inside your fridge or kitchen cabinets–you don’t want to double or triple your supply of fresh milk. Make it a point to do an inventory one or two days before going out so you don’t end up making this rookie mistake.
You go to the supermarket hungry.
According to a study, you're more likely to buy high-calorie types of food when you do your groceries on an empty stomach. Amy Yaroch, head of the Gretchen Swanson Center for Nutrition in Omaha, Nebraska, says you should avoid grocery shopping when hungry and when you don’t have a list because "you're just going to buy all sorts of junk food."
You use a large shopping cart.
Large shopping carts trick you into buying things you don’t actually need. If a basket is too heavy for you, there are small basket holders with wheels at the mall.
You don’t take things out of your cart at the last minute.
While you’re waiting in line, look over the items inside your cart and think twice if you really need them or if you just want them. Most of the time, people put items in their baskets without thinking.
You’re prone to impulse buying.
Ever wondered why there are always candy bars and small trinkets near the cash register? Because supermarkets know that there are people who are prone to impulse buying. Fight the urge to grab those chocolates for the sake of your wallet–and weight.
You don’t check your receipt.
Glitches in cash registries happen. If you're not careful, you might end up paying for something you didn’t really buy. Make it a habit to look at your receipt regularly.