Get your players to buy the pizza.
GMing is as much about running a game, knowing the system, doing dice rolls, etc, as it is about organising the night.
Food, drinks, seating arrangements, etc, are all very important to the flow of a game. As the GM, you're generally in the position to have the most control of it. If you know you're going to be getting dinner half way through the game - plan it so that there is a good time for intermission in the middle of your game.
I generally prefer a large round table for everyone to sit around if I can get it, but it depends on the number of players. You'll know your players better than us (I assume!) so you'll know what works best, but try to keep the...feng shui, for lack of a better term, in mind.