I also know who is most likely to have the best prices on common items.
The listowner has indicated that she makes up a monthly (?) menu and shops from that. I don’t. I look at the weeks ads and build a menu around that. If it’s cheap enough, I’ll figure out a way to use it.
(BTW, it really helps I’m only cooking for myself.)
I also keep a very large larder. If I had to, most of the time I could go without buying anything for 2-3 months. Would be rather boring, no fresh fruit, vegetables, or dairy products, but would be reasonably nutritious.