I wasn't self-catered. And, unlike my friends, I didn't have many take-aways or eat at the end of an evening. But if you start eating take-aways and post-nights-out, that can be something around £20-£30 a week. I avoid doing so for a variety of reasons.
I spent most of my money going out. There are other things that cost a lot of money though, such as washing (at Collingwood it was expensive), buying stationary and toiletries and maybe clothes.
Although, as I said, if you watch what you spend you can easily have a great time (as a fairly big-drinker) on maybe £80 a week; women and lightweights can expect to spend far less. It really depends, because if you start drinking at Riverside (at the DSU - before Planet/Revolver etc.) you can spend LOTS of money, also buying drinks actually at the clubs.
On a night out, maybe at Collingwood get a snakebite, two Skittles (with extra vodka/WKD or whatever instead of Orange) - then a few Double JD-Cokes halfway down the hill at the New Inn. Then Castle for some Turbo Smenergys. Then Jimmy As for a few triples (£2 on good nights) and then Loveshack with a few Woo-Woos or WKDs.
There's about £50 there maybe; you'll wake up not remembering much and seeking evidence on the course of the evening on Facebook.
Instead, you can stay at a lot of College bars down the hill and drink pints (£1.40 a pint means you're never going to spend that much), drink in your room (Waitrose has a very comprehensive spirit section) and so on.
It really depends on how much you watch what you spend. Hence the reason why there is a huge variability for Freshers in how much you spend; there a no (in essence) fixed costs living in (apart, of course, for the termly residence bill).
You're only a Fresher once. Most of my friends and people I know went out at least 3 times a week. You wont (I am led to believe) get away with this in the Second and Third years, if you want to do well.