Every grocery store has a few items that they sell at the cheapest price. Watch the per unit price of everything you buy and find the best price for each item. Some thing are seasonal like baking goods (including butter) and ham (Christmas & Easter). Bulk up enough when there is a good sale to get you to the next sale.

Costco is expensive on most thing. I only buy gas and English cucumbers from Costco. Everything else is cheaper at other stores.