Made from cardboard box, and packing tape as required. A serrated knife or box cutter is the only tool you need.
Cut slits as shown in diagram and push inward the edges. I left about 2 meters of cable loose (male end), which reaches the wall plug, then wrapped the remaining cable round and round the box. Finally I cut a slot which stows the female end till use.
Very easy now to transport, plug in, unwrap as much as needed, and re-wrap neatly when finished!