Wow, you must buy a lot of groceries!
Price Chopper (N.Y./Vt. supermarket chain) also has loyalty cards that pay off in gas discounts. There's much less to this than meets the eye...despite the name, PC's prices are on the high side compared to other chains, and the fuel points are only good at Sunoco stations, which are both few and far between and more expensive than most other brands.
I believe the points expire if not used within a certain amount of time.
I suppose if PC's the only supermarket in town and you have a large family you can save some money, but the whole thing is pretty deceiving.
No Krogers anywhere near me so I don't know how their system works.