I gave up my Costco card a few years ago, after comparing costs on things I buy.
It turned out the only things I saved money on were:
toilet paper (tiny savings)
eggs
Everything else cost less if I did careful sale shopping at the 6 market chains nearby. I have some excellent markets.
Now, if I bought brand name items, had a husband and 4 kids, and a large freezer plus root cellar, my decision might have been different. Or if my local Costco had organic foods and better meats. But I don't, and they didn't, so no membership. I don't miss it.
I do have a card for the local restaurant supply store, which is similar to Costco in some ways, without the rampant consumerism. Still, I go there less than once a year.