Being able to mark a card as "only purchases @foodstuff products", or being able to blacklist it from refilling gift cards would be the easiest way to close thi

Being able to mark a card as "only purchases @foodstuff products", or being able to blacklist it from refilling gift cards would be the easiest way to close this particular hole. If you could only purchase actual physical objects (ideally, only fresh food, rather than, say, a coffee-maker), that would go a long way toward preventing misuse.