Yeah I can’t get 5 different varieties of a ball bearings in the size I need delivered overnight from Costco. And for the things Costco or your local grocery store is great for, Amazon is often a far worse option. I noticed my wife was buying our toothpaste using a subscribe and save thing, so I compared it to our regular grocery store when I went shopping, and Amazon was like 20% more expensive. Great marketing on Amazon’s part getting people to assume it’s always the lowest price, but it’s often not.

The Trader Joe's model is an interesting comparison with the Costco model.

Similarities:

* Like you said, both have fewer choices than a conventional grocery store: if you want ketchup or peanut butter, there's only going to be one brand and one size.

* Both of them don't have scales at the registers: unlike at a conventional grocery store, nothing is sold by weight (which I'm sure provides another small efficiency gain).

* Both of them are cheaper than your typical grocery store.

Differences:

* I feel like Trader Joe's leans on store brand / white-labeling items more than Costco -- yes Kirkland Signature is a thing but Trader Joe's takes it further.

* The shopping experience is pretty different both in terms of the in-store experience and the quantities things are sold in.

* Costco requires a membership, Trader Joe's doesn't.

I wonder which elements of the two models would work best for a public grocery store.

As per their financials it’s roughly 50-50. I personally buy groceries and household consumables for the most part apart from the occasional electronics purchase.

IMO Costco’s food hits the sweet spot between high end grocery store quality and walmart level price.

I think a lot of people buy furniture and clothing on Amazon. It's extremely cheap and easy to return, or just throw away if you can't return it (not endorsing that).