Use a List When You Shop
There are two important strategies to employ when you go grocery shopping: Make your shopping list ahead of time and don’t go to the store hungry.
Not knowing exactly what you need makes room for impulse buying, while hunger can cause you to toss even more low nutrient foods into your shopping cart.
That’s why the best strategy is to plan ahead and write down what you need beforehand. By doing this and sticking to your list, you’ll not only buy healthier items to keep around the house, but you’ll also save money.
Source
Note: I use an app on my iPhone to make my list. It keeps me focused and cuts down the time spent at the supermarket.