While I was purchasing a rear fender for my winter bike, I decided to finally try out the famous Planet Bike Super Flash.
The .5 watt LED is extraordinarily bright (painfully bright, even). The light comes with a seat post clamp, a seat stay clamp, and a clip.
I've been using the clip. My Timbuk2 bag has an attachment point designed to clip lights to. Unfortunately, this was a somewhat precarious arrangement---and losing a $25 taillight would hurt!
So, I decided to strap a zip tie on it. The zip tie goes around the light, and around the bottom of the clip. This prevents the light from coming apart, the clip falling off, and the light from falling off of my bag.
I highly recommend this light. Remember, it is especially important to be visible in the winter.
Ride safe!
Anthony P.