Now, my shopping and eating are very regularized. But for many months, I planned meals, and made a shopping list based on those plans. I made sure to eat healthy foods just before going to the store, so as not to be so suspectible to the inevtiable temptations placed before us in the store. If you live in an urban area, services such as Peapod and Fresh Direct (NYC area) let you order online, hopefully lessening temptation.
Once in the grocery, I am suspicious of anything called “diet” food, or that carrier health claims. I’m always suspicious of added fiber – such foods often also have added sugar. For that matter, I’m suspicious of any food that has a bar code. The periphery contains produce, dairy, meat/poultry/fish… Things that often need to be refrigerated. As Michael Pollan says, healthy food is food that goes bad. Therefore, the stuff in the middle of the store that lasts for year on the shelf is probably not good for you.