Hiya!
Have you tried having a look at
Jobshop? I think that it isa brilliant student service to be honest, as they usually provide lots of jobs opportunities! They also offer job vacancies that are internal to the SU or the university itself - I find these the most convenient as the hours work really well with the student timetable.
Overall though, a lot of the jobs I've seen on Jobshop are things like bar staff, research assistant, catering assistants etc. There's also odd jobs, such as marking schoolwork or being an invigilator for secondary school exams.
~ Fatiha, Cardiff University Student Rep