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!
DIY Portable LEGO Kit with Free Printable Activity Cards. I like this for school, older kids can have activity cards to create planets/atoms/molecules/fractions, younger ones can practice fine motor skills.