Are you sure you want to do all English-language songs? I grew up in the Milwaukee area, and the songs we sang for Oktoberfest were all in German or macaronic (both English and German) - and people loved them. Maybe just a medley of German songs like Rosamunde (Beer Barrel Polka), Muss i denn, Schnitzelbank, Doktor Eisenbart, Das Wandern ist des Müllers Lust, Mein Vater War Ein Wandersmann (Happy Wanderer), Alt Heidelberg, du feine.