I agree with Ohio Farms. Take it from a guy who got his name on the map: take the phone.
I spent a good deal of my 20's and 30's doing things like backpacking, caving, and that sort of thing. All that was before I got my first cell phone. Someone back home knew where I would be, when I was going in, and when I was coming out. I had a set time that I had to make contact on Sunday night, otherwise they'd know to call the local authorities and report me missing. I also put a note on my dashboard.
Since we got the farm, I still make sure somebody knows what I'm up to. In spite of that, I now carry a cell phone. When I'm not the only one at the farm, I also carry an FRS radio. Here's why.
1) I'm 51. I'm in near-perfect health, but you never know. I'm getting to an age where I know people who have dropped over dead.
2) I hunt from treestands. I know folks that have had to crawl out on their elbows with a broken back. It sucks. I once had to do a quarter mile on my elbows, but I was in a cave and I was in peak shape-- it's not fun.
3) Even a broken leg or arm can really mess up your head. There's also hypothermia and the heat-related ailments. I've had it happen a couple of times. Once you've lost your rationality, there is no telling what you'll do. I got over-heated on a hike back in 2000, and nearly walked off a cliff in the Big South Fork. When something bad happens. It's great to be able to call and let folks know where you are.
4) KYHillChick has gotten lost twice on our farm. I've gotten turned around once. 'HillChick doesn't have much of a sense of direction. Me? What got me in trouble was the quick onset of thick fog, and the fact that I'd left the house without a compass. Getting lost can be a real problem. Couple that with rain, a small injury, and some bad luck and you can be mulch in no time.