The main objective is to look as neutral and nondescript as possible. Ideally, you should fade into the background.
I typically wear a button up shirt with a breast pocket, pants, and shoes. Avoid wearing anything that stands out or people can identify as a "signature" look. Not only work logos, but shirts with school, sports team or [recent/frequent] vacation logos should be avoided. I wear jackets with lots of pockets, especially hidden inside pockets for tip or house fee $$. I usually only have a $20 bill in my actual wallet (it avoids confusion). I also remove any work related stuff in my wallet, like ID or biz cards (which could fall out). Lastly, I typically wear clothes that are not what I regularly wear at work. In fact, sometimes I keep a "spare" [spa] jacket in my car. A dedicated "spa" wallet is not a bad idea either (now that I think of it).
Speaking of the car, don't forget to remove company related parking passes from the car (like visible hanging tags). Lose bumper stickers that allow people to easily ID your car. Black or white cars are best, as are ubiquitous models. If you ever have the opportunity to use a rental or loaner car when going, do it.
And, of course, put on sunglasses. Yeah, I'm a little paranoid.