Being new to the site, I don't know whether or not you do any machine quilting, but I use leftover small pieces to make little "sandwiches" so I can check my tension before I start on a project. If the little sandwich is big enough, I sometimes practice a new design or technique as well. I never feel like I've had to waste any batting that way.
I've also used small pieces to make coasters like some others here. :)