I would order online, but the stores I prefer to shop at either charge extra for online orders (e.g. Costco), or generally don’t have the best prices (e.g. local grocery). I wish I could easily comparison shop at Costco vs other stores, but that’s just not practical since Costco charges more for online orders even before adding in the delivery charge.
So I’m left to memorizing the per-unit prices of things I order frequently.