There are lots of ways to save money.
Either 241 offers (in Boots, supermarkets etc), you may buy same things online which may be cheaper, you may consider buying from sites that sell second hand products which are in good condition, look out for stores that give discounts for students (e.g.Topshop), or extra little gifts (e.g. McDonalds).
Also don't forget your student discount on buses and the tube, and you may also benefit from a student railcard, if you are travelling by train a lot.