Another form of scrap fabric is those wonderful strings. Sometimes they are left over from binding. Mostly, for me, I get them from squaring up my fabric. I will cut between 1 to 2 inches off of my yardage when squaring it up to use on a project. I do this intentionally to add to my string bag. Leftover jelly roll strips are wonderful too. They don't all have to be long because you will need short pieces to cover a corner if you are doing a strip quilt.