I ride alone frequently. Usually it is my commute to work-about 6.5 miles each way, but much of the year it is dark at least one direction.

I carry a pump, and two spare tubes (having had 3 flats in 10 miles not too long ago), and a patch kit. I don't have a cell phone, and while I have been thinking about getting one, I haven't missed it yet. I ride some residential streets, some trail, and some arterials, all on my commute. While I pay attention to my surroundings, I never give a thought to not riding alone. If I worried about things like that, I would never do anything.

Be aware of what is going on, but don't be scared of things.