you can buy all kind of food (the whole range starting at upscale Sprüngli choclade down to McDonalds) at Zurich airport fast.

Location of all these shops is two levels above train platforms, one level above the train ticketing desk) all these levels are connected with lifts and moving stairs.

In the train you pay about 3 (food) to 5 (soft-drinks) times more than at these shops.

When changing trains at Zurich aiport, have a piece of 2 SFr handy, to get a luggage card (the money is automatically returned if you can pt the cart back into one of many storage areas). You don't need that at Zurich airport (cards are free there - as people can't easilly remove and missuse them from there (in the middle of nowhere, where Zurich airport is ...).