I ride alone 95% of the time....I always carry my wallet with ID and Healthcard and my cell phone. Generally there are lots of routes around here in the East Bay that are pretty bike friendly. There are a lot of cyclists out and about so drivers are used to seeing cyclists. I also make it a habit (even in the heat) to wear my neon green vest when riding on the roads so as to make myself as visible as possible for drivers. In addition, I have a rear-view mirror attached to the drops (on the left) so that I can see what's coming.....I know it looks geeky on my Serotta, but I don't care what others think, it makes me more comfortable to see what's coming.

When I'm on my mtb and riding alone I stick with routes that are fairly well-travelled like Old Railroad Grade on Tam and tell my ex that I'm on the ride....