Quilts of Valor www.qovf.org
One way I do this is:
I always make a test block when I start a quilt. For years now I make the test block in red/white/blue. When I have enough I add borders if needed so they are all 12.5 inches square and VOILA, I have what I need for a sampler quilt. A bit of sashing and a border or 2 and off they go to a volunteer longarm quilter.