I hate waste. Hence:
1. I'm saving up all the little stuff that's too small to be sewn into anything to use to stuff a homemade heavy bag (...boxing/training). Seems that fabric stuffed together could get fairly close to the appropriate density.
2. Synthetic insulation scraps impersonating down? Could I use the shreds, small pieces, etc leftover from synthetic insulation projects like down? I.e. use baffles and stuff the pieces in? Obviously this would not have the full insulating capabilities of either down or synthetic, but for less weight-critical applications, it might work.