I have two major thoughts on this. The first one is to answer your question. For that I have a GPS based speedometer. The advantage of that are twofold. The first is that I have an exact (well, near enough to throw a rock to where it thinks I am) location.
I was working at a county Sheriff office once and I asked them if they were able to use the number if someone were to call in with a GPS coordinate. They were not; so, we set up a meeting with me and search and rescue to develop a procedure by which dispatch would be able to handle GPS coordinates. We developed the procedure, trained the existing dispatch staff, and made a instruction post that is now hanging on the office wall in the dispatch center.
Actionable Item: You might want to contact your county sheriff department and find out if they are also equipped to respond to GPS coordinates.
The second thing that my GPS speedometer does for me is more domestic in value. It can be used to generate a track that I can show on my computer. This enables me to show others, such as my wife, where I usually ride. Having an idea of where I normally ride would be useful if I were to need a pick-up on a normal day.
The second primary thought is that your list of fears included common things like flat tires. While flat tires are preventable, in that you can reduce their frequency, they are also a certainty. You should be riding with the minor tools necessary for minor roadside repairs. This would include all needed to repair a flat tire. You should also be prepared to tighten the normal nuts and bolts on your bicycle (pack a few spare screws of whatever size hold your fenders on too). There is one thing I would add to your list of tools and parts; Someone in this thread mentioned concern for being by the side of the road in the cold of winter making a repair.
If you call for a pick-up you will be standing in that same winter weather as you wait. As such, if you are not dressed suitably to walk out, you should add a chemical heat pack to your tool kit. you can use it to warm your hands as you change a flat tube; further, if you are heading home and get chilled (hey, if you are old enough, it just happens) it is there waiting for you.
So, route planning that includes sharing your route information, basic tools and knowledge of how to use them, a chemical heat pack.