The magician stuffs a silk handkerchief into a closed fist. When the fist is opened, the handkerchief is gone.
A handkerchief made from spun sugar (much like a two-dimensional sheet of cotton candy) is used. Such handkerchiefs last indefinitely when kept in a refrigerated magician's case, but if stuffed into a sweaty fist at room temperature melt away almost immediately, leaving the handy stick by visibly empty.
In an urgent situation, such as when the magician has been "vanished" by an assistant who can't remember how to un-vanish, these handkerchiefs can also be used as an emergency food source.