2 purpopses for lights To see and be seen. If you have bad roads and narrow tires, you really want a bright headlight to light your way. Now that I have a dedicated commuter with 35c tires at lower pressures, I don't worry about the bumpy streets nearly as much and I just have a blinky mounted on my helmet. I didn't realize just how helpful reflective sidewall tires are until I saw this pic that I snapped in broad daylight and apparently the flash was on on my camera phone

So after seeing that, yeah, reflective clothes help tremendously. I can go so far as to say that if I need to build another set of wheels for my commuter, I'll look at paying the extra money for Velocity rims with the Halo coating that look black by day but reflective by night, then I can run any tires i want and not worry about finding ones that I like with reflective sidewalls.
Depending on how long your commute is and how SOL you will be if you breakdown will determine just what you need to carry with you in terms of emergency goods.