Good old paper plates. I label the bottom of the paper plates 1A, 1B, 1C, 2A, 2B, 2C, and so forth. If it's going to be longer than just overnight, I will put them in Ziplock bags. I like the paper plates because they are easy to stack & keep together right on/next to my sewing table. I mostly use it for doing applique as I don't do a lot of intricate piecing.
If you are looking for something to label the pieces within a block as well, they make pins for that.