Add this to the stock at our fictional store: World's Best Bike! The store also features Amsterdam rear wheel locks, large saddle bikes, Egyptian spoke bells, Syrian beaded handlebar grips, and the Genuine Schwinn Transistor Radio Holder (part #00-628).
It's a New Zealand Bum Flap! You clip it around your waste and it sits right on your bum. Like a reflective vest, it's an easy addition to safety. It's light. It folds up into no space at all. But it's better than a reflective vest because:
1) It's quick and easy to take on and off. One clip. No velcro. No front and back and arm holes.
2) It's visible from behind even when wearing a bike bag.
And 3) you might actually wear it.
As far as I know, it's only available online from one store. We saw a lot in use in New Zealand. But I've never seen one anywhere else. And it's crazy expensive. US$30 not including shipping. I guess that's what "Made in New Zealand" means. And as my wife points out, judging from the lines in the sewing, "New Zealand quality" may mean made by New Zealand stoners.
I think it's best to make one yourself.