Become aware of what staples you use regularly in your cooking, and stop buying small packages and bottles of them when larger sizes are available. For instance, I'm always using a lot of soy sauce in marinades and meat dishes, so it makes no sense to buy a small 12 or 16oz bottle when I can buy 2 quarts at a much better price! Does your family go through a lot of mayo? Avoid the fancy little squeeze-bottles and go for a big jar, if you'll go through it all before its expiration date. I also buy staples such as flour, rice and dried beans in large quantities when I can, because they will last a long time and not go wasted in this house.
The trick however is to make sure your bulk food purchases are stored well - especially grains, nuts, flour and pasta which can get stale or even infested with bugs if not in good containers. Invest in some attractive, tightly sealing glass jars and canisters - plastic food storage tubs won't do the job! If you buy meat in bulk or so-called family packs, divide them up as soon as you get home, wrapping individual servings well in freezer bags before freezing.
What about Wholesale Clubs? Are they good money savers for buying in bulk?
Costco, Sam's Club, BJ's...some people swear by them, but I don't, at least not for grocery shopping. If you have a very large family to feed, perhaps you can do well at these wholesale clubs. But my problem is that fresh produce can generally only be bought in large quantities at a time in these stores - so large that my partner and I can never finish them all before they spoil. The meat in my opinion is not of remarkable quality, and much of the food products are prepackaged, frozen, boxed, canned, etc....not the kind of fresh and healthy eating we enjoy. So before you shell out the money to join one of these clubs, take a close look at the products they have available and whether you'd really be saving any money by joining - or just buying a lot of food you won't use and don't need.