If you are looking for things Costco doesn't carry, it is what it is. If your needs or desires line up with Costco's selection though, then there's no better place in terms of both price and efficiency of procurement.
If you find stuff from Costco is going to waste (namely foodstuffs, almost everything else they carry is non-perishable), just throw them all in the freezer. They will last months if not years.
This is where you get deeper into Wall-E territory. A lot of their "good stuff" is junk food. And a lot of people eat more of it when it's lying around their houses. And really it's only "good stuff" because it's brand name. There are better tasting chocolate bars with less packaging than Hershey's Nuggets.
If you get junk food from Costco, that's because you bought junk food.
But isn't the argument was that Costco carries good stuff?
The "junk" in junk food isn't talking about the quality (good/bad) thereof.