I just wear whatever I happen to be wearing, which is usually cotton in warm weather and wool in cold. So far this has worked for me, even on longer (40-50 mile) rides. I do have a yellow rain coat, though, and a 500-lumen headlight and one of those Planet Bike rear lights. So far, I have managed to avoid death, and even close calls have been extremely rare. But I rarely ride faster than 18 mph on flat ground, and my moving average is very much closer to 15 mph. I have a (totally unsupported) hypothesis that if you ride a little slowly, especially in heavy traffic, you're less likely to have a collision with a stupid motorist. (No, I'm not suggesting that all, or even most, motorists are stupid...)