Fork bag
If your fork has mounts for cargo cages it would be a waste to let that go unused. Not the most glamourous part of a bikepacking set-up but these bags add a lot of volume so they might as well look good doing it.
It is constructed with a floating liner, which means that water that makes it through the outer seams still is kept away from the contents of the bag. If you need absolute waterproofness I can tape the seams of the liner to seal them.
With 11x11cm and a rolled height of 30cm these come in at 4L.