Buy: Prescription Drugs
When Consumer Reports called more than 200 pharmacies nationwide for prices on a month's supply of commonly prescribed drugs, it found a 450 percent difference in cost between the highest- and lowest-priced stores. Drugs at big-box store pharmacies were much cheaper than those at many drugstore chains, especially if you opt for generics. Plus, you don't need a membership—warehouse pharmacies are required by law to remain open to the public.
Stock up on the warehouse version that comes in two large bags to a pack. You can save 60 percent on favorites such as Froot Loops and Honey Nut Cheerios by buying in bulk. Even organic cereals can cost 25 percent less at warehouse clubs.
Buy: Pet Supplies
Certain brands of dog food can be up to 60 percent less expensive at a warehouse compared with popular pet stores, so it pays to comparison shop for your pooch's favorite kibble.
Some warehouse clubs have partnerships with vineyards that award them deeply discounted prices for bulk purchases—which means you can save about 30 percent on certain wines. Warehouse store brands of other liquors, like Kirkland vodka, can cost nearly 40 percent less than premium brands like Grey Goose. Depending on your state laws, you may not need a membership to purchase liquor at a club store.
Buy: Men's Dress Shirts
Clothing is often deeply discounted but still of good quality at big-box stores. We've seen men's dress shirts at a warehouse store for 30 percent less than popular retailers.
Though it comes in large quantities—typically two 20-pound bags packaged together rather than a single five- to ten- pound bag—charcoal is usually less expensive at warehouse stores than at supermarkets. During grilling season, you're likely to use it up quickly. Even if you don't, charcoal has an indefinite shelf life if stored in a cool, dry place.
You probably don't use OTC medications every day, so that jumbo bottle of pain reliever might expire before you can finish it. Choose a regular-size bottle of a generic brand at your local drugstore or supermarket.
Skip: Cleaning Supplies
Liquid cleaners typically lose some effectiveness after six months to a year (certain powders may have an indefinite shelf life if stored in a cool, dry place). Unless you have a large family, purchase household supplies like window cleaner, dish detergent, laundry soap, and bleach in regular-size containers at retail stores.
Skip: Paper Goods
Common household items go on sale so often that supermarket discounts may be deeper than warehouse price cuts. Pairing store sales with manufacturer coupons can dramatically shrink your bill.
Supermarkets rotate sales on various meats so shoppers will come for cheap prices and then buy more profitable packaged goods. Manager markdowns are also often available when meat nears its expiration date.
Sources: Andrea Woroch, a consumer savings expert; Jeanette Pavini, a savings expert at coupons.com; Trae Bodge, senior lifestyle editor for the Real Deal blog at retailmenot.com; consumerreports.org; kiplinger.com; goodhousekeeping.com; today.com; womansday.com; thecouponproject.com; and thedailymeal.com