Budgeting for a holiday

calling3

I'm a newbie to this whole money saving thing and I'm trying to plan a holiday to Australia (leaving end of January) and a budget. I've got the basics like flight (already bought), accommodation, and eating but keep feeling there's loads I'm missing off. I'm paying for it on my CC (one of the Halifax 0% deals til May 08), with the potential to pay at least spending money directly from my current account.
I'm also owed about £600 from two flatmates which may or may not come back (although the likelyhood is it will) and at the moment, it seems to come to just under £1500. Can you guys give me a hand?

Thanks so much in advance,

Tash