Are you having a hard time changing your eating habits? Have you tried creating a meal plan? It seems silly at first but if you create a balanced meal on paper, and only buy what you plan to eat, the junk foods that sneak into your cart will start to dwindle to nothing.
You can find easy to print and fill out meal plans like the one below or just write it on some notebook paper. Start shopping only by your list, and avoid the center aisles of the grocery store-the healthiest items are typically around the outside edges.