I find both the C and the Y catering ex-LHR vastly superior to the equivalent ex-SFO. They are catered locally - if you look at, for example, the yogurt pots or the clotted cream pots, it gives the clue. It's only things like cans of Coke which fly around the world. As I understand it, they restock locally but don't take the inbound, unused stock off the plane. Whether they cater locally in small stations is a different matter.