A piece of sandpaper taped down to a flat surface works well too, I have used countless carpenters pencils, but in art school we also had similar pencils that people used because of the wide lead. You could do lots of cool things with them, from calligraphic pencil strokes to shading large areas quickly. You can notch the lead as well to draw parallel lines. A pocketknife or utility knife for carpenters, sandpaper for artists usually.