I like riding alone.
If I'm at home, I'm doing bike trail riding. I have my cell phone, food, various tools and a first-aid kit (as well as a spare tube and a small roll of duct tape) in my bag or on my person. I have my insurance card and driver's license in my jacket pocket (it has a zippered one), or in my camelbak pocket. I'm also in the process of typing up a cheat sheet of "basic on the road bike maintanence" There are also plenty of other cyclists on that trail, and most of the time, they'll help.

If I'm at school, someone (usually DBF) knows my route. I take everything mentioned above, plus my bus pass. I also tend to stick to doing loops on routes that are within walking distance of my building. A bit boring, but I don't know Cleveland that well despite being there for four years, and campus borders a bad area.