Leftover pieces of batting glued to pieces of foam core, cut to 15 inches square. Using them, I can lay out the pieces for several blocks, then carry them to the machine to sew. The fabric pieces "stick" to the batting, and seeing the layout while sewing means the seam ripper should come into play less often.
If you'd like some of your own, the link here or above will take you to Carrie's how-to for making them. Very easy, you really can't go wrong.