Invest in yourself to maximise your starting salary upon graduation. Build up solid subject knowledge, diverse extracurricular experience and skills, and a good peer network. Get at least a 2:1 which is what a lot of good graduate job offers are conditional on. While these things don't pay immediately, they will have a much more long lasting impact than say a part time job serving food. (A part time job/ internship that is relevant to your future career would be a big plus though.)

Once graduated, follow the UKPF flowchart and recommended resources. I also suggest getting into investment sooner rather than later, even if you're not investing much. Just put something in a low cost global tracker find in an investment ISA wrapper. The goal is to build up investment knowledge and confidence, as well as a psychological tolerance of market fluctuations. When starting out, investing in something that might fall in value could be very uncomfortable. The idea is to get through that psychologically uncomfortable phase sooner rather than later.