Marble Races with a cheap pool noodle (occupies the kids for hours.) Did this, but instead of cutting the pool noodle, the marble is small enough to fit inside the full noodle to roll down. Then can use the noodle for other things too!
Craft project: Instructions and patterns for making tri-tetraflexagons. Flexagons are folded paper polygons that have the neat feature of changing colors as they are 'flexed'. The flexagons in this project have three faces (tri) and are square-shaped (tetra).
DIY Nerf darts — when the original set gets lost (and you know they will get lost!), you'll be happy to know that you can make your own Nerf darts! Now it is known how to get the holes in the Nerf darts for legs on Proto X SLT quadcopter.