Retail work, bar work, tutoring and working in a cafe or restaurant have already been mentioned as suitable work for students looking to supplement their incomes whilst studying. There are also other opportunities available.
Look out for jobs on the university campus. Many universities offer part-time work for students, often in the Student Union or as ambassadors on Open Days. As an employer, you will find them very understandable when you need time off for revising or sitting exams.
If you are outgoing and popular, firms may want you to work for them doing PR work. For instance, you could work for a club helping to promote student nights. Firms will usually look at your Facebook and other social media profiles to see how many people you know, as they will be interested in getting as many people as possible into their club or buying their brand.
Child Minding could also create another work opportunity and may especially appeal to anyone thinking of working with young children as a career. You will no doubt need DBS clearance and if you have a car and a clean driving licence then this may also be an advantage.
You may also want to consider working at events. Sign up with an agency that supplies staff for big events. Whether they are business conferences, concerts or sports matches, there will be opportunities for bar staff, waiting staff and stewards. Agencies will often arrange transport to venues too.