I usually plan an adult Christmas party at our church each year. We do a sit down dinner because it is just simpler and easier to clean up after. It is less stressful than everyone getting up and having to stand in line to get food and having to look and look to see everything that is offered so they can make their choices.
Dinner's we have made do tend to more of an adult nature, like stuffed pork loin with orange glazed carrots and spinach salad. Sweet and Sour Meatballs with steamed rice, steamed mixed Fall veggies (squash and Zucchini like stuff), 5 onion soup. Chicken Parmesan with pasta, garlic green beans, garlic bread, side salad, etc...
But with youth I would do something like Spaghetti with meat sauce or a very rich and tasty Marinara sauce. Put Mozz. cheese and Parm. cheese on the individual tables, garlic bread can go out on the tables too. if you add a side salad, 2-3 oz. you can buy from a school or college food service and the lettuce will go a long way. You can do a veggie that would contrast the red and white main dish like green beans with some garlic and butter in them. That would be a simple meal and it could be made fairly inexpensive.
Where I buy my groceries:
If you have a local grocery store, one that has a meat market in it that still actually cuts the meat up then packages it, you may be able to talk to the meat manager about getting the meat at cost. I often got ours at a minimal cost. I got 104 chicken breasts for $40.00 for the Chicken Parmesan meal. I made the Marinara Sauce from scratch and then bought the slices of Mozz. cheese from the same stores Deli at cost.
I would go to Wal-Mart, and any other grocery stores in your area, NOW!!! Today, and ask for a donation application. They usually take 90 days to process it and get a gift card to you. They can sometimes do $50 but in this economy it may be less.
We always had a budget to cover the cost of the meal and I usually spent about $200.00 and fed anywhere from 100 to 125 on it. Buying in bulk at a local school can help too. Talking to the food departments at the food service kitchen at a local college can really help. The one local Jr. College always gave me everything at their cost because they ordered it especially for us, not for their food preparation, so no profit was expected. We had Lasagna and the college had frozen Lasagna noodles that were already cooked, I only had to take them out of the box and lay them in the pan, put the sauce and cheeses, add more frozen noodles, layers again, and repeat. And it only had to be thoroughly heated not cooked, talk about time saving...look around and see what you can find. talk to people who do this on a daily basis, the school cooks or head chef, etc...the food service department head, etc...
Have fun!