As an alternative to an "extra" with the bag, consider putting ties on the quilt in such a way that the quilt can be rolled and the tie pulled around either by conventional tying, with a velcro strip, or an elastic loop. Isn't this a way that some sleeping bags are contained? I have done this when traveling and want a small cover-up. It tucks into the overhead nicely when not in use or can become a pillow.