Couple of things:
1) Get out of the buying rounds mentality - it's easy - we do it - when it happens say "sorry, I'm saving for a big RTW trip and I just can't afford it" - everyone understands, particularly if you are a slow drinker - heck - I got out of rounds in large groups years ago - it just makes you drink more than you wanted and costs a fortune, and there is always someone who drinks something twice the price of everyone elses :-p
If they don't like it then it's seriously time to analyse who yoru friends are. I was stuck on a hellish holiday many years ago with some old friends from when I was at college (I'm 38 now). They drank like fish, and there were 12 of us. I'd end up going home halfway through the night as I'd be slaughtered. On the 4th day I removed myself from the beer "kitty" and they kicked up an almighty fuss - it was costing me a fortune - buying 12 drinks every night when I was good for 3 or 4! - I don't keep in touch with any of them any more :-)
2) - Not something mentioned much - one of the most important things to do, in my opinion, is open a specific savings account, preferably one that makes it a little difficult to withdraw from! - Once you put money in it it's safe from "you", accrues good interest, and it's very motivating to watch it add up each month. Leaving it in your main account is a recipie for disaster.
Cut up ALL your credit cards (you can get replacements later on)
Cut out dross like Sky tv
Pay off anyhting and everything you owe
Save like a loon - put the money straight in, and give yourself your monthly allowance in cash! - it's much much easier to keep control of your spending when you are a cash person. Using your debit card soon adds up - it's sooo easy to spend £5 here £8 there etc on misc. rubbish and find you've blown your budget halfway through the month.
Seriously, once your friends get used to you having a very strict budget they will understand, and more often than not, be helpful.
I'm leaving for approx 3 years in Jan 08 with my wife. We paid off our wedding, and £15k of cards, then saved. 18 months later we have £60k - it's a lot easier for couples to save tho - staying in is as much fun as going out! :-) - and we were quite high earners. But if we can do that much with debt, all in 18 months, it shows what can be done - and we used to spend every penny each month on general "stuff"! (and we have a mortgage)