My take on this: get pretty colored index cards and colored pencils, crayons, markers, etc., and each person or group gets a card to decorate and sign for you. Then they can pin it up to a board, or tape it to the wall, or something. Later you can put them in a photo album.
"Who Wears the Cake" Game - stick out the champaign glasses (or whatever youre using) with the bride & groom names. Whoever ends up with more money, gets the cake shoved in the face when they cut it! Love this idea (& Easy way to get an extra buck for the honey moon!)