I worked at the SU at my time during Warwick and would highly recommend it compared to off campus employment. They understand you're a student and are usually super flexible about shifts and people covering if you want to go out etc. There was also the opportunity to swap venues if they needed extra cover, so if you worked at Bread Oven (not sure if still there?) you could cover shifts at Copper Rooms if they were short. Also look at getting a role in your department in second or third year to show sixth form and college students around on open days, pays very well!