Here's a fairly simple one.
If you use the plastic strapping and it becomes loose for some reason, there really isn't any good way to re-tighten it because once the tool that pulls the strap tight cuts it off too short to re-use that tool. I made a real simple winding tool to apply enough pressure to the strap to pull it tight again.
The winding tool is a piece of 1/2" OD steel tube with a slot in one end for the strap and a 17/64" hole drilled in the other end for a 1/4" bolt to act as the handle. A short piece of 1" square tube is also required to push against the retaining clip. I ground quarter-round slots in one end to keep the winder centered.
To re-tighten the strap, the loose end needs to be threaded through the square tube and the slot in the winder. Turning the winder will re-tighten the strap.