Pick something that you want to give away. As the evening is going on, randomly hand out fake money for showing excitement, asking good questions, showing interest in booking a show...anything you want. Don't tell them what the money is for and at the end of the night, tell them to count their money. The one with the most money gets to take the prize home. (last week I gave away a retired sample from my kit)
You can get fake money in any toy aisle.