High-vis vest - absolutely positively utterly mandatory. If you have to chose between a high vis vest or a helmet, chose the bare head every time.
You can get them from Harbour Freight or whatever, if your sporting goods type place doesn't have them, ask to order some. Get the yellow ones with reflectivity material (Not the 'melted glitter' kind). Here's a link to one:
http://www.harborfreight.com/cpi/cta...emnumber=94701
Mirror - I've tried a helmet mirror, I couldn't see a damned thing through it. Ever see one of those puzzles where they take a picture of something, then make you try to identify it by looking at some little fragment of a booger of something in an obscure portion? That's what a helmet mirror is like, except that if you guess wrong or take too long figuring it out, you wreck. Don't do it. Get a bar end mirror, a big one. Convex if you can find one. You need this mostly so you can check to see if someone is coming up on you easier, for lane positioning reasons. Just glance at it if you think you might need to take a little more lane to avoid a hazard, or if passing width seems to be getting sketchy.
Lights - the best you can find. Dinottes or similar, probably.
Then chose roads so that you have high visibility front and rear.