This is a classic frugal tip that is so good, it bears repeating. Supermarkets aren’t a good place to buy toiletries and many household consumables (diapers, paper plates, deodorant, etc.), so only shop the perimeter.
Most grocery stores are laid out in a “box” pattern with vegetables on one side, dairy and meats along another (usually the back, due to theft concerns) and breads on the other side. Anything in the middle falls into one category or another:
1. Make it instead
2. Don’t buy it at all
3. Buy it elsewhere.
The one area that I stray is with pasta. One store we go to keeps it with bulks in the back—another with ethnic foods in the middle. I’ll run around and get some pasta—even though it’s easy to make at home.