This is my favorite because it is so easy and can all be made in advance! Grill (or if it works better) fry either lots of brats, or even various different kinds of sausages. If they are raw sausages, I steam them in a bottle of beer with an onion or three (depending on how many you are cooking for), then either grill them or let the beer cook down and add a little oil (depending on how much oil was int the brats to begin with) and brown. Toss in a can or jar or whatever of sauerkraut.
Some things are great from the can and save for some effort. We live in an area where there are a lot of Germanic people and if you do, you can buy purple cabbage in a jar. It isn't something I buy for myself because it is rather sweet.
I used to make German potato salad from scratch, but at some time you realize your acquaintances don't have that great of taste buds, and I can buy canned that everyone likes just fine. In fact, I lived in Germany as a kid, and don't think I ever, ever tasted "German" potato salad! The German dish I most associate with Oktoberfest was something I think was called kneudel or something like that. I think it was mashed potatoes, eggs, and maybe other ingredients, but not much, mixed and wrapped in cheesecloth, tied, and immersed in boiling water. It was then taken out, cooled, and sliced. In fact, I didn't like it much, my sisters refused to eat it. I tried to make it once, just for the h of it and it was OK. But, really, that is the one dish I remember from eating at Grunwald, outside of Garmish during Oktoberfest.
Big pretzels are ideal. You can buy them in the freezer of your grocery store and bake them for only a few minutes (I think I've nuked them with success). If you have children coming to the party, you can tie a ribbon around them and put them over the kids' heads and let them walk around with them (Yes, we did that at the real Oktoberfest in Munchen).
When I was a kid, the food at home was simple, because we went out during the day to watch and listen to oompah bands and folk dancers. And yes, I did part of it on military installations, but unlike many military acquaintances, we had German friends and spent the holiday with them.
At the Oktoberfest tents, there would be a whole OX on the spit in the corner. How amazing is that?!
By the way, Oktoberfest ended in October, mostly was in September. I think my husband said it has to do with a calendar change.