I do the same thing, collecting the scrap batting in a specific tub, then when I am organizing projects to sandwich to quilt, I pull out the larger scraps and if they need a little more, zig-zag scrap batting together until I have a large enough piece. There is always batting leftover after doing a larger quilt, but I finally learned to put the leftover batting directly in the tub and it saves a lot of aggravation, so it's there when I need it.