Heads or Tails Game
Choose your prizeChoose an item for your that will appeal to as many of your attendees as possible. A good rule of thumb is to pick something at least as valuable as the ticket price. Keep the ticket price in line with the demographics of your audience. It could be anywhere from $5 to $100. Expect about 25% participation.
Sell the ticketsYou can sell actual tickets or use someting more visible such as a gold star that can be attached to their bid card or name tag. You might even use glowing bracelets or noisemakers to heighten the level of interest.
Play the gameA good time to play this is near the beginning of the event but before the main speaker or auction. Now your auctioneer will ask all of the participants to stand. They will select either "heads" or "tails" by putting their hands on their heads -- or their tails/hips! The auctioneer flips a coin and announces whether it is heads or tails. Everyone who matches the coin flip will remain standing. The others will sit. To raise more money, you may want to offer a one-time buy-in for everyone who was eliminated in the first or second round. This continues for a few rounds until there are only 3 or 4 participants remaining. These finalists will move to the stage for the last few coin tosses, until only one player is left standing and is declared the winner. Check out this video for a live example.
Here is another live example.