How far out on your own? Riding alone is not the best idea, but I do it alot too. I would always make sure someone reliable knows where you're riding and when you expect to return first off. As far as tools, I agree a cell phone is great unless you're in the mountains. An I.D. is good so they can identify the remains if it goes bad.
I carry a tire plug kit and co2 charges. A multitool, zip tie, 8-10-12mm wrench, two allen wrenches(can't remember sizes), and a tire gauge.
If you are going quite a distance get a camelback pack with water bladder and some power bars. GPS too
In my case, I'm thinking of a desert race which has 80 mile laps. It's hard for me to predict what's most likely to go bad that I could service on the spot and get moving again. Recovery vehicles do come around, but it takes hours.
Last year, I had a cellphone and camelpack. When the battery died, I realized I didn't even have a tool to disconnect the leads. On the other hand, I wouldn't have a spare battery anyway.
Maybe this idea is a lost cause from the get-go. Maybe anything that I could "fix" with such little supplies would just tear apart again in a few miles?