Backpacks

[eash]

This could probably go in Shopping too but as it is to do with travelling I'd thought I'd just keep it here.

I'm going travelling/backpacking to Oz in June but need a back pack and am in desperate need but because I've not done the travelling thing before I don't know what to look for when I go back pack shopping. Can anyone help please? Like how much am I going to have to spend on one? How big? How many compartments should I have? etc. etc.
Any help will be greatly appreciated.
Thanks

[befuzzled!!]

i've never been backpacking before but after living on the banks of loch ness for 6 years you see quite a few.
backpackers usually have big bags to hold EVERYTHING they need and because you are going to oz you will probably need a water thing in it.
my advise is go to millets or blacks they'll help you out as they are professionals