Great uni, about to get a lot bigger too with the new Heslington East development. Doesn't have a students union building but each college has a bar although they recently limited the days each one opens. Lots of clubs to sign up for in freshers week, everything from paintball to karate.
Its easy to walk into the city from the campus or you can use space age no. 4 bus. As for nightlife there are only a couple of clubs, neither of which are very good. The main one is the Gallery which is ok. There are millions of pubs though so you're bound to find one you like. Closer to uni there is the Charles where most undergrads go, and the Deramore which is more of an old mans pubs but has much better food. York has all the main highstreet shops. For food there is costcutter on campus which is pretty awful, but there is a new Safeway just off Hull road near the uni or Sainsburys at Fosse Island near the city centre, both of which are walking distance. I'd recommend getting a bike though.