First I pulled out the entire stack of 'fabrics to be used for backs". Many of these had small - or large pieces (see the story of the 2" squares mentioned a few posts back) cut out of one or both ends. I straightened the ends, and stripped out the part I cut off. Then I trimmed off the selvage. Most pieces measured 21" from the fold to the edge after trimming. A few of the oldest fabrics were a bit wider, and some measured only 20". As I trimmed I stacked the pieces according to widths. Some were big pieces, and some were small - sometimes only 1/4 yard - once I straightened the edge. No matter - they all work for backs.
Once I trimmed a stack I started sewing them together along the crosswise cut. This doesn't look like much in the picture because these were pieces little more than 1/4 yard each.I sewed until all the fabrics of the same width were sewn together into a long piece of "new fabric". Then I cut the "new fabric" into the appropriate lengths needed for the quilt backs. I always put horizontal seams on my back now that I have a longarm - they roll better on the rails this way. For the two postage stamp quilts I needed 3 strips of 80" and 3 strips of 69". I cut the proper width strips, stitch them together and press the seams. The backs are quite a bit longer than needed when done this way - that's OK - I just trim off the excess after quilting and put the remainder back to become part of another quilt back in the near future. Some of the fabric combinations may look a little crazy - I don't care. These backs are for quilts that will be used up - everyday bed quilts for us or the kids and charity quilts - not for heirloom creations.
Once I made backs for the postage stamp quilts I stalled out - too many things needing done for Christmas. So the rest of the stack waits in the sewing room, where I'll prepare more "new" fabric after Christmas. When I finish the first of the two postage stamp quilts I'll post a picture of the back - that will help you visualize this better.