Chocolate Story, as someone who lives in York I tend not to pay that much attention to the touristy stuff, but I was impressed when I went last month.
Railway museum, meh, I'm not that interested in trains but is is free and good if you like that kind of thing.
Minster, amazing inside and out. If the weather is half decent a walk round the walls gets you some good views of the city and is free!
Art Gallery is pretty good (again, if that's your kind of thing). Yorkshire air museum is good as well, but that's just outside York.
What kind of food do you like, there are loads of nice places to eat in York.
Dave