Look at your grocery list

I shop for the week to help budget and I hate side trips to the store. It also keeps me from picking up junk food on a side trip. When you write down your grocery list, it should contain tons of fruit and veggies. You also should be staying on the outside perimeter of the market - where the produce, meat counter, and dairy is. Rarely should you be in the aisles with the pre-packaged and prepared food when you want to eat clean and healthy. (Except for maybe pasta/grains and canned/frozen fruit and veggies).
Having a list and sticking with it for the week helps you budget your calories, balance your meals, and if you're like me and you stick with just the list, you won't be adding snacks and junk food to your cart.
(I write out my list so it's in order of the way I travel through the store, produce is first and takes up most of my time/money)