At least 2 people, ping pong balls, cups and some beer.
First you need 4 people (two on each side of a table) and ping pong supplies then you will need 10 cups (plastic party cups work great) and a beer keg at the ready.
You have to put the cups in a triangle shape and fill them up or leave then half full (your choice completely).
One person on one side of the table serves the ball. If it lands in a cup the player on that side of the cup drinks the cup up beer, then so on. The loser's have to drink what's left on the table - have fun!
Even though the games called beer pong, you don't have to just use beer, you can certainly use your imagination with this one.