Pro tip: If you don’t care about perfect-looking letters, you can paint on a t-shirt with acrylic paint. Just put cardboard or a paper bag or something in the shirt to keep the paint from bleeding through to the other side. Dries quickly. Once dry, goes through the wash just fine. Never run out of letters. Especially Qs. :-)
Unfortunately, I don’t have great handwriting, nor a steady enough hand to use stencils.