I save all the broken crayons (remove paper), and when enough accumulate, we melt them using an iron (a piece of wax paper goes between iron and crayons and another piece between crayons and towel), then I pour the colorful mess into chocolate molds or schnapps cups, let it harden, and voila! New, multi-colored crayons!
(My oldest once suspected me of being too stingy to buy new crayons, but I asked her why we’d want boring single-color crayon sticks, when we have interesting-looking multi-colored ones?)