I used to buy everything at Costco. Giant bags of spinach. Gallon jugs of olive oil. The spinach would rot before I finished half. The olive oil went rancid after eight months because I could not use it fast enough. Bulk buying saves money only if you actually use what you buy. Here is what is worth it and what is not.

Yes — Buy These in Bulk

• Toilet paper and paper towels: They do not expire. You will use them. The price per roll at warehouse stores is significantly lower.
• Rice, dried beans, pasta: Shelf life is essentially forever if stored dry and sealed. A 20-pound bag of rice costs what 4 or 5 small bags cost at a regular grocery store.
• Laundry detergent and dish soap: Non-perishable. You know exactly how fast you go through it.
• Canned goods: Tomatoes, beans, tuna — shelf life of 2+ years and you will eventually use them.
• Frozen vegetables and fruit: They last a year in the freezer and are often flash-frozen at peak ripeness, so quality is actually better than “fresh” out-of-season produce.

No — Never Buy These in Bulk

• Fresh produce: Unless you are feeding a family of six or plan to freeze or can everything immediately. A 5-pound tub of spinach is a race against time.
• Cooking oils: Oil goes rancid. Olive oil lasts about 6 months after opening. Buy the size you will use in that window.
• Spices: They lose potency after 6-12 months. That giant jar of paprika will be flavorless dust by the time you are halfway through.
• Whole wheat flour and nuts: The oils in them go rancid. Store in the freezer if you must buy bulk.