I love Costco. I’m single and live alone and it’s still a great deal for me.
The biggest thing is fruits and vegetables. Around here, most of the grocery stores have either bad quality or insanely expensive produce, unless you always just want the standard cheap stuff (bananas, onions, baby carrots, etc.). I eat a lot of fruits and veggies every day, and it just gets expensive. I am happy to buy the things that I like in large quantities. They also have a lot of exotic things that I can’t get at a local store (at least not in at all similar quality, or price) during the various seasons of the year. I go in, see what looks good, and buy 2 or 3 big bags. Most fruit or vegetable stores for a surprisingly long time in the fridge.
I also use the dairy foods a lot. The Greek yogurt they carry is outstanding and a staple at my house. There’s a huge price advantage in things like good quality cheese, too (or the little single serving cheeses I use a lot when losing weight). I also like the bakery for things like the sandwich slims. Whole wheat bread is often cheaper on sale at the local grocery, though.
Frozen foods is another good area. I eat a lot of fish (I’m a former vegetarian who now eats seafood), which also gets expensive – check my location, it’s not like I can buy local – and the local groceries tend to only put the flavored / battered / cheap stuff on sale. I like to get things like salmon burgers, tuna steaks, bags of shrimp, and so on. I have a deep freeze which came with my house, so big bags of frozen fish don’t adversely affect me. Big bags of frozen vegetables are often also a good deal, though there’s less selection than in fresh. Also, if you’re throwing a party, the frozen appetizers are awesome!
I don’t shop as much through the dry goods. Once in awhile I will pick up something (giant jar of capers $5, at my local store a tiny jar is $3.99) but it needs to be something I really like or will store well. Things like cans of black beans, cans of soup, etc.
The thing about Costco is that they rotate out stock so by the time you’re done with that big case of soup, chances are they have a different kind now. This can be frustrating if you find something you really like – I still check for that mocha-flavored protein drink every time, and it’s been gone for a long time – but it does mean that there is a lot of new stuff to try. I’m not a terribly picky person so I’ve never gotten something so bad I wouldn’t eat it. Also, they rotate the samplers through a lot of stuff so you can try a lot of things ahead of time if you visit often.
The things I tend not to buy there are protein bars and shakes, which for some reason have a far inferior selection to Sam’s Club, and things like cleaning supplies or paper goods, which you can often find cheaper elsewhere and in less ridiculous quantities. I do like their no-scent detergent though.
Do I overspend? I can’t remember ever getting something I didn’t use, other than occasionally spoiled produce if I forget I have something or get really busy. I don’t get things in quantities I know that I’ll never use, like condiments. I mean, why? If it takes me a year or two to get through a normal size container, I don’t need six containers. I guess I do have some salad dressing hanging around that I need to get through, but to be fair, my mom twisted my arm on that one since she said it was so awesome. I guess you just have to think, “will I get through ten pounds of flour in the near future”? If the answer is no, don’t get it. But not all things are in such quantities – milk is in gallons, for example. But to me, the point isn’t so much buying in bulk, but that Costco just has better stuff and/or better prices on the stuff I eat a lot of.