Shopping for cheap groceries

I spend more time than necessary shopping for cheap food, and I think I'm good at it.  I sometimes think that I should write up a guide to buying cheap eats in my area (Western Contra Costa County, CA) because I see so many people who don't seem to know how to do it.  I've seen people at the dollar store with 50 items in their cart, most of which are junk: frozen meals, for instance, which aren't a good value to begin with, and which are probably  cheaper (by weight) at Grocery Outlet or FoodMaxx.

I suppose this has been done elsewhere, but I guess that's no reason not to do it myself, if I think anyone will be interested.