Getting around the town of Wacken is pretty easy. There are maps available on the official Wacken site, so you'll be able to find your way around the festival, and also to the exit. From there, it's basically a "turn left" deal: the town's center is uphill to the left of the festival entrance, so while it's a decent walk, it's also hard to miss. In town, you'll see the yellow sign for the Edeka on the opposite side of the road from the festival, and then a little further up the road you have the town's two banks, Sparkasse and Raiffeisen, which have their ATMs usually accessible. You'll also see a bit of local color with the signs advertising drinks and stuff in people's front yards, but the prices are barely better than the festival, and if you don't speak German, it may be a little difficult communicating. Here in what used to be West Germany, nearly everyone speaks at least some English, but in a little farming town like this one, they don't get a ton of practice. This is basically all you need; everything else is within the festival grounds.
Customs and other inside baseball
In Germany, people don't generally tip. This is because there is a 16.5% VAT (value added tax) included in the price of everything that you buy from a human being. This is why you don't see tipping at the infield bars. Also, you don't need to worry about figuring tax on stuff you buy from stores; all taxes are included, so the price you see is the price you pay. What we call a cellphone, people in Germany and Scandinavia call a 'handy'; there is a handy charging station at the festival main office (on the road up towards town), which you may not otherwise associate with mobile phones. Not that your phone is tremendously likely to work anyway; in Europe the cell standard is GSM, and most phones from North America still don't respond to this standard. Most people in Germany can discriminate between individual Americans (who are people like them) and the policies of the US government (which nearly everyone considers irrational and destabilizing), especially at Wacken where people who make their way from other continents get extra respect for their dedication, but it's still not smart to go running around in downtown Hamburg in an American-flag shirt yelling "USA! USA!". Act like a metalhead, not a tourist.