Interesting thought experiment.

What do you think about storing some water in the car? On the one side, it's the most critical resource after wound treatment and shelter - you won't survive more than a few days without it. Also, if you're just semi-hibernating in a closed environment (and possibly cough recycling), you'll need much less water than normal so you can realistically keep enough water for a week or more. On the other side, most "stuck in a car" scenarios (at least in the northern hemisphere) involve rain or snow, and if they aren't and they last a month or more, your water reserve won't save you.

I keep a bottle of water too. Yes, I think realistically the only reason that I'm stuck that way is because of a blizzard. Melting snow is going to be the solution. In any case I think given I don't die right away, the best chance to be found and rescued is to have a radio transmitter device. So the cell phone, even when it doesn't work, is the next most valuable thing. There are tons of stuff we can do with the cell phone or ham radio. Kim was searched for, just that they couldn't find him. I think being searched for is the most realistic scenario if something like that happens to me.