I have hosted many LAN partys in my day so here are the things you should have
1st: All the extra computers you can find(aka that old lap top you put in the attic)
2nd: no cd cracks for all your games( no one likes swapping disks non stop)
3rd: Food
4th: drinks
5th: lets of different types of games, go to a thrift store and pick up lots of old but yet fun titles