Catching up on old friends is the main activity of a class reunion, but you can add to the fun by planning a variety of games and activities. A reunion will be enhanced by not only remembering the past but also by adding new memories. When you begin gathering data and preferences, look to your classmates' input as a way to decide what kinds of events will make the reunion special for all who attend.
The first reunion activity needs to revolve on finding as many alums as possible and getting input from them on their expectations and ideas for the reunion. A website is a perfect vehicle for accomplishing these goals; you can create a totally new site, use the school's site if they agree or go to sites already established for that purpose such as www.creativereunions.com and www.reunions.myevent.com. You might consider including a priorities list and asking those who might not want to get in on the organizing to simply check reunion activities that have the most appeal.
Reunion organizers often prepare nametags for participants, with both names and pictures from the high school yearbook. These nametags give everyone something to talk about from the minute they walk in the door. In addition, you might jumpstart conversations by asking people to wear a different kind of tag on their other lapel: a badge featuring a tiny world map on which they mark in red the spot furthest from home they've lived in or visited. Try setting up a graffiti wall (simply cover a wall with butcher paper) and start a dozen columns, each with a teacher's name at the top; encourage everyone to jot down a couple of classroom memories on the wall.
On your reunion website, ask for volunteers willing to participate in a "living memory" presentation and find someone willing to serve as the host for the presentation. These mini re-creations could include a clarinetist playing his senior year solo, a re-enactment of cheerleader tryouts, a duo re-creating an experiment that almost blew up the chemistry lab, a few thespians portraying a scene from a school production, a mimic doing an imitation of the principal, the valedictorian giving part of his or her graduation speech and so on.
Reunion trivia gets everyone involved by dividing alums into teams. Ask for volunteers to create questions ahead of time and then (since they already know the answers and can't play), to serve as moderators. Create a giant board based on the design of the school and let correct answers move players around the board. Come up with categories of questions such as classes/teachers, the athletic program, other extracurricular activities, songs that were popular during graduation year and miscellaneous (who can remember what the cafeteria always served on Mondays, for example).
Scan as many candid photos from the yearbook as possible, especially those with several students pictured together. Make enlarged copies of these, as well as other photos you have collected ahead of time from class members. Post these around the room as the evening progresses. Then encourage classmates to pose in groupings identical to those in the old photos. (Mary on the left, Margaret in the middle, Dan, seated, on the right, for example). After the reunion, post pairs of old and new photos together on the website or make arrangements for alums to buy copies.