I wish stores would consistently advertise unit price, like the cost per oz/ml/g. My local store does a pretty good job most of the time, but sometimes they’ll have different units listed for competing products, which makes it so much more difficult to compare.
I have a feel for the prices for most of our common purchases, and I try to remember them in terms of unit price instead of package price (e.g. a decent sale on granola in my area is ~$0.20/oz, fancy granola is more like $0.30/oz).