Ok, so I know this is totally random (that is the name of the page after all) but I found this wonderful recipe for homemade washable sidewalk paint:
1/2 cup cold water
1/2 cup cornstarch
about 15 drops food coloring (more or less depending on the intensity of the color you're going for)
Slowly mix the water and cornstarch together keeping the lumps to a minimum. Once all the water and cornstarch are completely mixed, add the food coloring (I did mine 3 or 4 drops at a time to get it to the right shade). The paint is ready to go! Once the kids (or you ;) ) are done using it, simply store in a container with a lid. Because the water and cornstarch may separate between uses, make sure you stir it before each use.