Alone most of the time.

Many of you have made the point that someone knows where you are, and that's good, but it may not matter in a true emergency. You might not 'go missing' until hours after you need the help.

Many of you also mentioned having a cell, but remember that it's not a substitute for a first aid kit and some rudimentary survival gear.
Ever try to stop arterial bleeding with a cell phone? Start a fire with one? They're great, but they should complement your basic gear, not replace it.

Stuff happens.