Buy: Organic berries
There is a single exception to the fresh produce rule. It is organic berries! When they are in season, Costco offers good prices on them. Berries do wonders for your health, but they can be rather pricey.
Skip: Flour, baking powder, and dried yeast
Baking ingredients such as baking powder, dried yeast, and flour all have a limited shelf life. You should avoid buying them in bulk because they have a tendency to go bad quickly. It is much better if you get them in small amounts instead.