i'm planning on taking 450 quid or so on holiday with me for 12 days (with hotels and flights already paid for).. these things often work with one staying up so late at night that breakfast isn't a major option really, and lunch isn't that big a deal. if there are cooking facilities where you are, you can budget by making pasta and other random things.
also, if there's a supermarket nearby, get some alcohol from there. obviously you don't want to go out clubbing clutching a local grocery bag filled with stella cans, but if you get 6 packs of random drinks, some orange juice and vodka from a supermarket, and have some before going out, you can save money on that front.
i'm sure that it's easy to spend whatever you've got, but you should be able to do a week away for... 300 euros i'd have thought. so something like say.. 250 quid for a week should be fine.