Buy a guest book (kind of like the ones at wedding receptions) for attendees to sign when they arrive.
In addition to their name, you might ask them to write their address and phone number as well.
Then, as the reunion winds down,
ask them to enter a comment about their favorite moment at the reunion
("When dad got dragged through the mud during the tug of war").
Collect these books from each reunion,
and have them available for laughs at future reunions.