I have this situation with Nectar points at Sainsbury's. I pay the full cost of the fuel and use the Nectar points against my shopping bill. Quite simply, the fuel (well most of it) is tax deductible and the shopping isn't.
By Jove, you've got it.
We save our nectar points.
Spend 'em once a year or so.
Last year, bought the boy a play/treehouse thing. Over £300 quids worth.
Getting a few bits and bobs won't be memorable but a big thing (like the playhouse) seems like a better freebie.
(If you can afford to, obviously)