I have had warethouse memberships since the 80’s, including Price/Pace, Sams and Costco. At present Costco is my only choice. Being in the mid-Pacific, we pay more for many items because of shipping logistics and we are a tourist location. Fuel costs are high too.
Costco here offers a reasonable cost for items and in some cases, a real bargain. An example from this week is Kings Hawaiian Sweet Rolls normal price is 2 packages for the price of 1 pakage at Walmart. Costcos rotisserie chicken is half the price of local (vendor at the side of the road) chicken.
Before COVID, Costco was $1 a gallon cheaper than the next higher station. Recently that gap is a lot narrower. Still it saves me money for gasoline for the farm and ethanol-free gas and diesel that I use for the farm.
I keep an eye out for deals and during a remodel, found LED lights for my ceiling at over 90% off.
There are a couple of things which are not a deal such as xases of soda. In an unusual condition, some of the meat offered is a lot more expensive for me at Costco. I helped a neighbor set up a Co-op for pet food. We buy meat directly from the producer and many of the items are a lot cheaper and we don’t have to buy in bulk. We might pay $8 for something sold for $12 at Costco. Our meat is USDA inspected, local beef (unlike Costco). The same beef goes to restaraunts, supermarkets and even our local hospital. All of them pay more than I do.
I was working for a (gasp) timeshare organization (I was front office and we did not sell timeshares there or else I never would have set foot there). Each Monday morning we had an orientation where activity vendors came to explain their trips and events. I would go to Costco on Sunday and buy fruit, melons, bagels, pineapples, sweet rolls and so on. I used my credit card and was reimbursed for the cost, thus making a ‘boatload’ of extra money in my rebate check from Costco. Oh, and a few times I had to buy air conditioners and other items for room at places like Lowes and Home Deport. Those charges also went on the Costco card.
I buy items that can be frozen like extra milk. In some cases I can buy items and exchange them for other things with a neighbor. When I buy a Caeser salad I end up having to eat it fairly quickly or it goes bad. If I buy a large bag of frozen vegetables I tend to eat more of them to try to use them up. Although that doesn’t always happen, it certainly forces me to eat more vegetables than I normally would, so I guess that is a good thing. Compare that to the 5 pounds of assorted mini bars of candy I just bought. Too bad we don’t do Trick or Treak here, so I guess I’ll donate the remainder with friends 
All in all, I like Costco, probably spend a bit more than I want to, but certainly save money over local prices. I am pretty good at looking at the unit pricing both there are at chain supermarkets.
I forgot to mention:
When I worked at the Condo/timeshare, people checked in on Saturday for a week. Many would head to Costco for things like snorkle gear, liquor and bulk things like water (assuming Hawaii was a 3rd world country I guess). Anyway, they often checked out and left all sorts of stuff. Some was donated to places here and some I guess was retained by the cleaning staff.
Visitors would head to Costco and buy all sorts of Hawaiian shirts. You could tell many of the visitors because the whole family had the same shirts on. I guess it was easy for them to ask if someone has seen their kids who were wearing the same shirt.