Ultracheap but very metal living:
go to Wacken town "Edeka supermarket" (aks peop´les where it is everyone knows but basically ones you go to Wacken town just follow the streeam of peoples down the only road)
buy lots of german Bratwurst in biggest available package I think they have 1 kilogram package
bigger than this but did not find better picture
buy cheap toast
+
they also have american toast but its usually a few cents more expensive so go with regular one
Toast and Bratwurst combo will also make you able to drink more its very good.
buy 5.0 beer BLACK
because its world cup it might also look like this its the same as the black one:
its not the best beer but average+ for good price
DO NOT buy this red export variant:
it tastes like piss
You can also buy very cheap barbecue sets there. If you want to go cheaper ask your neighbours if you can use their barbecue often that works and you can offer to at least get some coal or so and its always a good way to socialize. Many Germans coming to Wacken bought way too much stuff in preperation and are too well equipped and are actually happy if they can use all their stuff and help you out.
Only drawback here is that you might have to walk a few times to carry all your groceries depending on how much beer you need.
Edeka also has more healthy stuff like fruit and vegetables to complement your diet and basically all else you might ever want but that is more expensive of course but if you got extra budget.
Good thing for taking beer to the festival area:
You can buy 1 litre big wacken "Maßkrug" (very durable but light plastic transparent beer stein). If you get that the first day in Biergarten (go early because later the big ones are sometimes all in use and you cant get one if you are unlucky) you can use that the whole festival and bring beer (or a litre of rum+coke+lemon+ice as I do when its hot) from campground into main area and they dont take it away from you. Its also a nice Souvenir to bring home. If you have a belt you can easily store it there when its empty and band is playing as it has a handle:
