I have set aside some ugly fabrics to use in practice sandwiches. I like to work with a 1 yd. piece of fabric, and I'll sew two half yard pieces together if necessary. I don't bother stitching together the binding scraps if they aren't the right size. This gives me an ample amount of space to experiment, and once I've determined my design, to practice it before I start the quilting on the quilt. I usually buy my batting large so there is leftover and I can practice on the same batting that is in the quilt I'm practicing for.