Almost all of the roads around me are unlit. I was driving one winter evening when I saw a flashing rear light (dark clothes, no reflectors or hi-vis, pitch black), and I was on him before I knew it - no fixed point to judge distance. Since then, I always make sure I have a constant rear light as well as a flasher.
Agree with the helmet light as well. I also use a micro front light (bought as an emergency back-up) on the handlebars turned to face me so that everyone can see more than just a front light at junctions - you'd be surprised the effect and difference it makes.