I went to a baby shower recently, so some of these might be applicable: everyone was asked to think of a reason why the mother-to-be would be a great mom beforehand, and everyone wrote their answers in a special journal at the shower. Also make sure someone has a camera, and it can be fun to do a set of special pictures. I took pictures of everyone's shoes, since everyone had really nice shoes on. You might have everyone making a goofy face.
Also, something I like to do on vacations with a group is come up with 100 memories (just one liners, like "The flight was delayed an hour and we got free drinks"). Someone has to be the list master. It's fun to do 100 because you have to really think back and come up with misc details. I love going back and seeing everything that got written from the trip, it really brings it alive. Maybe this could be changed into a shower game, like 100 memories of the future bride and groom by the guests or something like that.
And remember to have fun!
