Meat: ~anywhere it is at a low price...Keep up with what prices are good and don't buy above those rock bottom prices. I like to buy some meat at our local salvage store. The meat is still in date and not bad. This week I bought .99 chicken breasts and $1.99 ground beef from IGA and BiLo grocery stores. We have been blessed with deer meat, of which we prefer over ground beef!
Dairy: ~ Sam's Club has the be prices for dairy, particularly cheese.
Vegetables:~ farmer's markets and produce stands.... Aldi grocery store as well. Better than that, your garden! Side note here: Frozen vegetables are generally cheaper than canned ones. Canned ones contain a lot of water and that is included in the ounce factor. A 15 ounce can of green beans, etc. is not 15 ounces of green beans. It's probably half beans and half water. 15 ounces of green beans in a bag is just that.
Grains: ~Buy in bulk through a co-op or know your price per pound prices and compare.
Any other goods: ~ Shop your sales! Know your prices!
Sweets:~ Yep, of course this should be mentioned! Who doesn't eat sweets? As for baked goods, make your own from the ingredients that you buy at low prices. Candy? Check dollar stores such as Dollar General or salvage stores.