I used to store just the tops but that was before I retired. They were mostly simply pieced scrap quilts so finding a perfect binding was never an issue as almost any colour would work. Now I'm finishing up many (ok years worth) of BOM's and if I can't get it quilted as soon as I have finished the top, I store it with the backing, binding and pillowcases (I always make at least one or two to store my finished quilt). Then I either machine quilt it (on my Juki or my friend's LA) or give the whole stack to my guild for Community Quilts or QOV. I was lucky that I always stored enough fabric with the unfinished pieced blocks that matched for the binding and borders.