Buy: Batteries
Do you have items in the house that need batteries? If so, you must know that it is not exactly cheap to replace them when they run out. When you go to Costco, you might as well buy batteries in bulk. A pack will be enough to keep your electronics powered for a long time. On top of that, the prices are much lower than items from other brands. The Kirkland brand is made by Duracell, so quality is guaranteed!
Buy: Milk
If you have five children and three cats that drink a lot of milk, go ahead and buy those Kirkland gallon jugs of milk. However, you need to ensure that you can finish the entire thing before it goes bad. A lot of websites tell you to avoid it, but there is no harm if it is gone before it spoils. As a matter of fact, this is a good way to keep your bones strong and your wallet fat and full at the same time.