When I cut pieces for blocks, I store all the pieces for one block in a sandwich bag (the kind that just folds in - since it's cheaper than the ziplocs). I then keep all the sandwich baggies in either a drawer or a tote bag. When I work on a block I put it back in the baggie until the block is assembled, and then I put it with the finished blocks in the tote. That way, I can pull out a project, work on one block and, whether I finish it or not, everything for that block stays together.