Be seen. This is the advice I have for you. Especially if you're a crazy winter biker in the City with No Sidewalks (that would be Anchorage, Alaska in the winter when snow is plowed onto all horizontal surfaces).
A tail light for your bike can save your bacon, and Princeton Tec has a great one. The Swerve is waterproof, crazy bright, and has mounting options for your seatpost, seatstay, handlebar, fork, basically anywhere you want to clip it. The mounting mechanism is basically a solid rubber thingy that you can easily move around or even between bikes quickly.
Two Maxbright LEDs provide both solid and blinky modes with the flip of a toggle that's easy to operate by feel alone. You can forgo the mounting assembly and just clip it to your seatbag if you want, just make sure it's level to get the best visibility. Drivers will have no problem seeing you anywhere in your 180 degree rear sector. The advertised 70 hours burn time on two AAA's is roughly accurate. The Princeton Tec Swerve is handlebars-down the best tail light out there.