I always have my cell, and always have it on.
I guess the main way I stay safe is by riding known roads, in daylight. And these roads are used to having bikes on them, so most of the drivers are bike-friendly too...
I have often thought about making a pepper spray of some sort, but I never get around to it.
I don't off road except on our farm, so don't have to worry about mtn-bike trails.