Target sells a type of Christmas light that fits very well on my bicycle.

Philips 30ct Christmas LED Dewdrop Lights Battery Operated Multicolored SW

These lights are simply a strand of highly flexible wire with LEDs on them attached to a battery pack with a switch.

They offer lights in a variety of colors, but I went for the traditional blue, green, orange, etc., colored lights.

They're about 9 feet long and I found that they fit perfectly around my frame.

The lights say they're for indoor use only, but I found they survived rain, snow, and harsh Chicago wind and cold. On two AA batteries they lasted all December and are still going strong into January. These gave me a lot of illumination from the side on dark Winter evenings.

A little electric tape did the trick to secure the battery compartment to my seat post under the saddle. I also used electric tape to secure the wire around the frame. If I had a rear bag under the saddle I could have just as easily tucked the battery compartment under there.

The light mode can be toggled from off to blinking to slowly fading to staying on constantly.

I was afraid the wire could come loose while I was riding and get caught in the wheels or drive train, but thankfully the tape held fine and that was never an issue. I imagine zip ties would have worked well too.

For a cheap easy way to get some seasonal lights on your bicycle, I think this and similar products work great.