DH and I were at an upholstry shop to get pads for camping and I was surprised to see a HUGE room of fabrics. Some were heavy but many were not. I bought 3 pieces to cover the pads (sneaky, because we only bought 2 pads) and the last piece just "happens" to be big enough to back a queen size quilt. It is a pinch sturdier than regular quilting cotton and a fraction of the price. And wide enough to be used in one piece.
One way to use up strips of left over fabric is to piece them for the backs of quilts. You can put different blues together, prints with solids, etc. It doesn't take much time because you can make them large (or simpy just use them w/o cutting if they are the "right" size). The danger of this is that sometimes you may see your quilt on your daughter's bed with the back side up. "I like to change it sometimes and enjoy this side too." Oh well. People used to put plain muslim on the backs and you can still find some at quilt shows today. Piecing is even better.