We're diehard Costco fans. There are a few things we like at Sam's and it's a less-hectic shopping experience. When we see a sale on a Sam's membership, we'll buy it in one of our names, then we let it expire. Next deal, we buy it in the other's name. We don't like Sam's enough to own a continuous membership. Ours doesn't have a gas station, and they've stopped selling propane tanks/refills, which used to be a great buy.
Funny, I just ordered some socks on Amazon this morning, because I wanted to buy exactly what I wanted and not have to go out and shop for them, plus their price was excellent.
To your list, I would add Grocery Outlet, especially on Senior Day. I also check out the Costco Returns store occasionally, but only if I'm in the area.
I will miss the 99 Cents Only Stores to my dying day. This is primarily because I used to be a vendor and earned a lot of money selling to them, but I also loved being their customer.