Paint balls, for practice fighting... Because lets face it, violence should always be the absolute last resort--even in a simulator.
With paint balls, you don't have to actually kill your enemy, or force him to jump out of his plane. You can make your point with a few well-placed shots, snap him a salute, and fly back to base, satisfied in the knowledge that you've bested your opponent--and that both of you will live to fight another day.
Before anybody starts spouting off about ballistics modeling, please spare your breath. This is a simulator, afterall, and we can retain standard live-ammo ballistics even with the paint balls... Sheesh, guys.