Do you have a crockpot? Throw in a roast, a ham, a bunch of chicken wings or legs, or any other meat. Have some of 20+ attendees chip in for the main dish instead of bringing a side.
As mentioned before, do a food bar. Taco bar, baked potato bar, salad bar. Have a hot dog bar if you eat hot dogs/brats.
Have lettuce wraps. Basically sandwich...