I just grab whatever from my bag of goodies and as long as it isn't the same fabric as something else already in that block - and it's long enough to fit for the next piece, it's golden. I don't care if it "clashes" as when the block is done and used it's so colorful nobody sees that. I also use some selvages sometimes to add a little kick. Some people don't like them- but I think they make it "SEW" interesting! When I cut my blocks I sometimes can use the scraps for other strings or for crumbs. My waste really gets used until it goes into the doggie bed bag because it is just too small for the crumb bag. I'd just sew strings and crumbs and be happy forever.........