In addition to lots of reflective material and a good headlight, I recommend the super-bright [Dynotte 400R tail-light][1]. 

![alt text][2]

This light is the brightest I could find commercially available and seems to be visible from more than 1/2 mile away in bright sunshine (and much further at night). I ride with it on at all times of day while commuting year round. 

In my side-by side tests the 400R was significantly brighter than my car's break-lights. In the past 8 months I've had about 10 comments from drivers and as many from other cyclists about how bright the light was.

  [1]: http://store.dinottelighting.com/shared/StoreFront/default.asp?CS=dinotte&StoreType=BtoC&Count1=787059962&Count2=704200387&ProductID=91&Target=products.asp
  [2]: https://i.sstatic.net/sbaWj.jpg