This is such a great idea for Matt's PhD Graduation Party in 5 more years! or the kids graduation parties later on. Instead of guest signing the picture at a party. Have everyone one sign a puzzle piece and show who was a piece in your special day.
A homemade Lava Lamp? I'm not sure it could get much better. A little bit craft, a little bit cooking, a little bit science and a whole lot of fun! Come Together Kids: 10 Crafts and Activities for Boys