I'd suggest a two-way radio as well, either a CB radio or a ham radio. It's probably preferable to have both if you have the room, since CBs and (most) handheld ham radios generally use completely different frequencies that will carry in different ways and different directions. (You technically need a license for a ham radio, but in an emergency, the laws are clear: You can use any sort of transmitter available to you in a life or death situation, whether you'd be authorized to use it normally or not.)
We've got 'em, though, just in case they might work. With that and the cell phone it's pretty good coverage. The CB is just 11 meters and not much coverage at all.
It was mentioned in articles that On-Star or Lo-Jack would have helped as well.
You can buy a handheld aviation tranceiver for a couple of hundred bucks. With that you can talk to any airplane in your line of sight, including airliners flying over. If you put out a mayday on one of those radios, you would probably be heard by a dozen airliners right away.
all Art Bell regulars know of the wind up radio w/ led light .Am ,FM , Shortwave and weather. GPS available too
about a buck ninty
We now notify people on both ends of our journey or at intermitent points when we should arrive there. Two ways, cell phones (but not necessarily reliable), flares, mirror.....waterproof matches. In other words, look in a scouting manual.