I bought some of these at costco:

http://www.amazon.com/Sylvania-DOT-S...0016844&sr=8-1

They were like $10 of them for $5, I keep them in my pack or bag, and it's something that I can just tie on the bike or strap with velcro to have a blinky.

Also - have a blinky light on your bike. You can get fancy ones, but there are cheap ones as well.

The planet bike superflashes are really bright & get good reviews:
http://www.amazon.com/Planet-Bike-Bl...8600598&sr=8-5