Like what?! I doubt you'd want to go and use anything on your own, and if you have friends at a particular college it's usually not a problem. A number of bars will ask you to be signed in by a college member, ditto bops (some are open to non-college members, sometimes you have to pay a bit extra...), you can eat at another buttery or formal but will need a college member to put it on their college bill. I can't think of any other facilities. Some colleges only open their gardens to college members, or have designated college areas of the gardens. I doubt anyone would mind if you sat in another college's TV room. Laundry facilities are usually locked away, ditto pigeon holes if you wanted to post something through CUSU-UMS. You could stroke another college's cat...