Tour the Past—I held a reunion one year at the church where the grandparents of all present were buried. We also took a 10 minute journey to the cemetery where the parents of origin parents and grandparents were buried. In addition, if the house where they lived is still standing, you could tour it {as long you as receive permission from the owners in advance}.
Oral History—turn on the video camera and allow each person to share their memories. You could either have one area to record each person individually or do a round table conversation.
Memorabilia table—I keep a memorabilia table that hold pictures, the family Bible and a compilation of the family research. I also have a PowerPoint of family pictures going on the computer.
Heritage Cookbook—I know many families that compile recipes that have been passed down, combine this with some stories and pictures and create a cookbook.
Photo Swap—have everyone bring family pictures that they can share. If one person is the family historian, s/he may want to have a scanner on hand to scan the pictures.
Memory T-Shirts—many families create T-shirts to wear. If you’re going to hold the reunion at the beach, amusement park or another busy area this is a great way to keep track of one another. 
Family Tree—at our reunion we honor the parents of origin and their 10 children. We recognize those from each family. Often we have the family tree up with each family member or the parents of origin and their children {if the family is extremely large}.
Family Timeline—create a family timeline on boards to put up filling in basic information and dates {including births, marriages and deaths}
Food for Thought—most family reunions have food. This is the best way to bring people together. Decide in advance if you will have a potluck, meet at a restaurant or have the event catered.
Specialized Theme—create different themes each year {ex. Prominent ancestor, 1950s, Presidents and First Ladies, Movie Stars, etc}. present awards for the best costumes and innovation.
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