Wow, I wish I'd found this site when I was 15! I'm 28 now (tend to be a lurker, not a poster), but just to echo what others have said, definitely get a credit card at 18 but ALWAYS PAY THE BALANCE - it does help with buying a house - we live in a stupid world where you need to use credit to get credit.
Also, don't worry too much about student loans - you'll have realised that it's WAY different in the UK than it is for our US friends.
Part-time jobs are great (I had good success working in a cafe and doing the "cosmetic catalogues" thing, which was really flexible) but not at the cost of your studies, obviously.
I hope you manage to save and FIRE under 30, many congrats on being sensible and forward-thinking (I was good with money at your age, but had no idea of the possibilities of FIRE until much later!).