I've dropped one of my fuel caps from the top of the wing and came close a time or two more while re-fueling. A lot of planes have a chain that keeps the cap tethered to the filler neck to prevent this. Thinking Cub Crafters might have this as a spare part I called Vera who checked and called me back saying that they didn't offer a chain like this.
Does anyone know of a source? The cap has a small hole on its underside for a clip to attach like other caps I'm familiar with. What is needed is the chain and the part that snaps inside of the filler neck and a small clip.
DSCN2168.jpg
Here's an example of a Cessna tank and cap with a chain.