I've done the A/B test. Costco saves my family 25% across just food, ignoring other stuff I get there (batteries, shirts, jackets, shoes, underwear, deodorant, etc.)

You're pointing out that you need to plan properly to bulk shop, since you're necessarily modeling future consumption over days/weeks across multiple people, but that's different than over-consumption. It means you have to be analytical and plan, but that's exactly how we do it.

I despise the city living lifestyle, where folks jam themselves in tiny grocery stores to buy 2oz containers of jam and mustard because they don't have enough room to actually fit the food they want. My sister and dad live this way in NYC, and it's annoying as hell every single time I visit them. Wanna throw a meal together? First step: leave the apartment.