@ Cogline
If you plan to stay at the festival area I would really recommend you to bring your own tent and a sleeping bag, unless you're planning to rent a car or something else that you can sleep in.
Or if you could manage to find someone that has a big enough tent and spare a place for you.
Is seems that it is a rule that it will rain on festivals, so I would not recommend you to sleep "under the stars" so to say.
Regarding what alcohol that is sold, it's mostly beer but I do sort of remember a whiskey stand as well, but I wouldn't swear to it.
If you do bring your own bourbon, you may pour it into a "Wacken mug" before you enter the festival grounds, but you may not bring the bottle. At the camping grounds you may have as many bottles as you like though
Cash is always good, you'e bound to find something cool to buy that cost a shit load of money and to come with a credit card don't work that well. The line for the money machine is really not worth experiencing either.
This year I had to go and get money, I think I spent about two hours in burning sun before I got up to the machine, missed almost all of Immortal due to it as well.
There has been other Aussies at Wacken though, even some that hang out at the forum from time to time, you might get more answers from them.
Cheerz.