I study at Warwick! Apart from when there are larger organised events on, you don't generally see little stalls as you describe around campus. Whether this is because they don't allow them or because no-one has thought of doing this yet I'm not sure. Most probably it's the former.
It's perfectly possible to get to Coventry and Leamington from campus - buses vary from about every 15 minutes or so to every hour depending on the time of day and day of the week. Mostly these are to serve those students who live off campus in 2nd and 3rd year.
In terms of jobs available, I don't know much about off campus but from what I've heard, on campus jobs can be very competitive to apply to. Some are available through the SU and there is also Unitemps which handles temporary employment with the university.
Edit: just noticed you mentioned small towns. Warwick University isn't actually in Warwick - it's on the edge of Coventry.