Here's big fun for families, protestors, and families who protest! At Instructables, friedpotatoes explains how to make massive sticks of sidewalk chalk with plaster of Paris, tempera paint, and a Pringles can as the mold. From Instructables:
We mixed roughly 6 plastic cups of plaster powder with about 4-5 cups of water for a good pourable plaster mixture. The exact proportions aren't super important, just make sure that it isn't too dry or too thin, err on the side of it being too dry so you don't have to worry as much about leaks. If you want to make colored chalk add in about a half a plastic cup of tempura paint into the mix before adding the water. Make sure the paint you use is non toxic and washable, so you don't stain the concrete or harm the environment. Paint marketed towards kids usually meets these standards.