We don't have a Costco here. We do have a Sams Club. I've never bought a membership though. Sometimes I'd go there with a friend who has a membership and buy a few things with her card.

Now, my workplace has a Sams Club Card that employees can borrow for personal shopping. Have to pay in cash though. I go periodically to buy a few select items that I can't find cheaper elsewhere.

At Sams Club you don't have to be a member to use the optical store or the pharmacy. I sometimes buy contacts there.