anything reflective is really important, but make sure you're also wearing light clothing, so a driver can easily identify the glowing object...

I ride with yellow lenses at dusk and at night. The yellow reduces the glare from street lamps and oncoming cars.

Make sure you're paying close attention to the road, as cracks and bumps are far less visible... I didn't realize how much I use my periphery when riding until it was so dark that I had to really focus in order to avoid cracks (and a possible crash).