Other than being in a game with people whom you can trust and truly be yourself... I would have to say awesome food. When your players celebrate the game so much that they don't just use it to de-stress and ply on everyone else their negativity, or worse, find ways to channel the game into a weapon to sexually harass another, or attack another person for gripes or issues caused by different games (note: examples based on some threads I've read having happened at Gen Con), you have players who take the effort to make the meet up even more special by bringing something to share with everyone else.
Those games mean a lot when they happen. And while I can't say more without breaking certain agreements I've made, I can say I'm happy to know there have been enough instances where such sharing has happened in games I've been part of.