I have also had people recommend using store-bought shortbread rounds or other cookies with a flat bottom, turning them upside down to practice outline, flood, and decorating. I never tried that, but think it's a great idea. That way you can at least eat the practice cookie. (I also save "old" cookies to practice on - they are in a plastic container clearly marked "do not eat - old cookies" so my kids don't think they can get at them!)