Buying in bulk can save you money or it can waste money. Here’s how to do it right.

“The questions to ask are: ‘Do I need it? Do I use it? Do I love it? Can I store it?’ ” says Kathryn Broullire, a teacher and food blogger at Worn Slap Out. The Potomac mother of two dismisses the idea that bulk buying means buying in massive amounts. “A bunch of bananas purchased at a warehouse store is no different than a bunch from the grocery store, except they’re cheaper. And my family can eat a rack of lamb in one sitting.”

You don’t even have to go to a warehouse store to buy in bulk. Many supermarkets, big-box stores, online retailers and even manufacturers now sell family packs and bulk quantities of everything from chicken thighs to paper towels to batteries.

“More of us are working from home and consuming more, so bulk buying makes sense. There are deals to be had, but a lot of people inadvertently waste money,” says Leah Bourne, managing editor of the Money Manual, a personal finance site.

The key to successful bulk buying is simple reverse engineering. Look around the house. Take inventory of what you use the most, don’t tire of and have an ability to store. Work backward to create your shopping list. Explains Bourne: “Is there something you drink every day? For instance, I like a cold-brew coffee that costs $4 a can. I found it online for $1, so I ordered 100 cans.”

Adds dealnews.com consumer analyst Michael Bonebright: “Don’t buy for the person you think you are going to be. Buy for the person you are. In other words, don’t buy 100 frozen fish fillets if you aren’t going to eat them. The items that you put in your shopping cart every week are the ones you should buy in bulk.”

Do stick with things you can open and keep fresh or, if you forget about them, can open later and have the same product experience.

Do look for food or products with a shelf life longer than six months.

Do check expiration dates.

Do take climate into consideration. Do you live somewhere that is extremely hot or cold? Is it humid or arid? Humidity can cause mold and clumping, while low humidity can spell trouble by drying out products.

Don’t buy a new-to-you product in bulk. First try a smaller size, even if you have to pay a bit more.

Don’t buy 10 pairs of reading glasses or clothes to wear three years from now. Our bodies change.

Don’t assume that just because you buy it in bulk at a warehouse store, it will last longer. Products have the same shelf life no matter the point of sale.

Here are some of the best and worst things to buy in bulk, so you don’t waste money.

Canned goods. There’s a reason our grannies canned and pickled vegetables, jams, jellies and more. They don’t spoil.

Frozen foods. The freezer can be your friend. Vegetables, meatballs, tortellini and similar items gain an extensive life span when frozen. Take large packs of meat, break them down into smaller portions and repackage in freezer bags or aluminum foil (also a great bulk buy) for the freezer.

Coffee beans. Ground coffee will go stale in a few weeks, but coffee beans in an unopened package (no need for a freezer) are fine for up to nine months. Whole-bean coffee has a higher upfront cost than the ground stuff, but that’s why buying in bulk is so critical. You’re getting a better product that lasts longer and you still benefit from bulk pricing, Bonebright says. Note: If you are preparing for the apocalypse, instant coffee can last up to 20 years.

Wine. Bourne says you can get high-quality wine in cases by buying directly from vineyards, who then ship to your doorstep.

Cleaning products. All-
purpose cleaner, dish soap, laundry detergent, disinfecting wipes and similar items retain their efficacy. Use a funnel to refill smaller, easy-to-use containers. Store dishwasher or laundry pods — designed to activate in water — in a dry place, so they don’t disintegrate. There is one surprising cleaner (see later in the story) that you don’t want to buy in bulk.

Personal-care items. Toothpaste, toothbrushes, dental floss, soap, shampoo and razors shouldn’t spoil. If your tastes change — say you tire of a specific shampoo — you can donate the excess to charity.

Paper and plastic goods. Toilet paper, facial tissue, paper towels, trash bags and plastic storage containers last forever. With paper goods, opt for quality over quantity, Bonebright says. Cheaper paper products tear easily and don’t handle liquids as well as fancier brands, which means you’ll probably use them up faster. Still having trouble finding paper products in local stores or through online retailers? Look to the manufacturer. Companies such as Georgia-Pacific sell directly to consumers.

Over-the-counter medicine and vitamins. Be sure to check the expiration dates for pain relievers, allergy medications, eye-care solutions and vitamins. If given the option, choose a tablet over a gel caplet, which is more likely to break down over time.

Contact lenses. Your prescription probably isn’t going to change within a year. Order a 12-month supply instead of a three-month one. Many manufacturers offer a discount if you do so.

Office supplies. This includes pencils, pens, dry-erase markers, highlighters, staples and packing tape. Buy office paper by the case instead of the ream and have it delivered, so someone else does the literal heavy lifting.

Batteries and bulbs. Store batteries in a cool, dry place, and they should last for years. Rechargeable ones are the best value. Lightbulbs are another good bulk buy.

Pet food. Canned pet food typically has a shelf life of up to two years, while unopened dry food lasts about 12 to 18 months. If you are buying big bags of dry food, transfer the food to an airtight container to keep it fresh and so ants, rodents and other critters won’t get into it. “Snakes actually love cat food,” Bonebright says.

Gift cards. Warehouse stores often sell gift cards in bulk. At Costco, you can typically buy $100 worth for $80. And there’s no rule that you must “gift” a gift card. Keep that 20 percent savings for yourself by buying cards for your favorite stores and restaurants.

Deli meat. Don’t buy more than you can consume in one week. Once open, it goes bad quickly. The same goes for shredded cheese, which, once exposed to air, may start to mold.

Spices. Except for salt, most spices become less potent and flavorful over time.

Baking ingredients. Broullire bakes every other day and still wouldn’t buy a 25-pound bag of flour, as it easily collects moisture. The same is true for nuts and cooking oil, which may go rancid before you use them up. The one exception is vanilla extract, which has a long shelf life.

Condiments. Do you really need tubs of hummus or a gallon of mayo? Unless you and your family are going to consume ketchup, mustard, salad dressing or spaghetti sauce on a daily basis, you may be better off buying condiments as needed.

Brown rice. White rice is a true pantry staple, but brown rice will go bad in about six months because of its high oil content.

Soda. After three to six months, it loses carbonation (goes flat) and the flavor changes.

Bleach. Who knew? The one thing you think should last forever starts to degrade after six months and isn’t as effective at killing germs.

Cosmetics. Powder-based makeup has a longer shelf life than gels or creams, but once opened, products can become contaminated with bacteria. Mascara is notorious for lasting barely three months after its first use.

Sunscreen. The expiration date on sunscreen is real. Ingredients spoil, and the product will not effectively do the job of protecting your skin.

Laura Daily specializes in consumer advocacy and travel strategies. Find her at dailywriter.net.