Get free condoms
You’re all going to be having loads of sex, amirite guys? And being modern, responsible, 21st-century types, you’re going to be using condoms. At a tenner or so a box, that’s going to be a serious income drain. Or it would be, if you couldn’t get them free from your university or the government.
Your university SU will have welfare officers who can give you some, or more likely a big box full of them that you can just make off with. Meanwhile your local sexual health (GUM) clinic will give a bundle and throw in a free (recommended) STI test. Failing that, at most freshers fairs, people will literally be wandering around chucking them at you.