Heads and Tails is a popular game to use as a segue from dinner to the live auction. It is easy to play and always entertaining.
Guests “buy a ticket” to participate. The Auctioneer or Emcee asks everyone that is participating to stand and explains the rules: The object is to guess a coin flip. Participants are instructed to commit by placing their hands on their head or on their “tail”. The coin is flipped, and all those that got it wrong sit down. And the process repeats until there are only a handful of contestants left. Typically, the finalists are brought onto the stage for the final round(s). The game continues until there is a winner.
Some auctioneers/emcees like to offer the finalists an opportunity to “stop now and share the prize - or continue” before each coin toss (any agreement to stop must be unanimous) - which adds to the “theater” of the game.
Many events increase the revenue potential of the game by allowing people to buy multiple chances - this variation is usually tracked by providing a string of mardi gras beads for each ticket/chance. When they lose a round, contestants remove a strand of beads then continue playing as long as they have a stand of beads.
If the game is played as a single chance/ticket game, it is most common to provide a signup sheet on each table. When the Auctioneer/Emcee introduces the game, guests are instructed to signup on the sheet in order to play.
What this person wins is up to you. Most common is to share a portion of the Heads and Tails “pot” - provided as a credit to spend at the auction. I have also seen it where they win a special gift certificate for dinner or tickets to a popular play in town. This game is a good one to get the guests up and moving.