I use waxed twine to bundle similar things together. For example, I cut up hundreds of plant labels from mini-blind slats. They were messy until I bundled each size together and bound them with twine. Now each bundle is like a tidy brick.
Maybe he could bundle similar lengths or similar materials together, then stack them or stand them up in a smaller footprint.
But then you have to untie a bundle to pull out just one thing.
Or tie them so loosely that they flop around.
Or you can wrap some heavy paper, cloth or plastic around the things, bundling them loosely but keeping them aligned. THEN tie string around the wrapping to keep it wrapped.
Maybe drive big nails part way into the walls and lay wires on top of the nails.
You could have multiple rows on each wall. That will also keep them off the floor.
