This is one of the main reasons you should try to keep fit and in good health, and be able to bike (or god forbid, run) 20 miles or more without
stopping. Keep in mind all the stuff you'll be carrying, too.
This is a good point and is often overlooked.
Fitness is a big thing. In the event that this scenario does occur, traffic will
be snarled. I would take the approach of driving as far as I
can, then abandoning my car and setting off on foot or bike. This will require some level of fitness if you want to survive.
Get used to extreme weather. There no telling if or when this happens what the weather will be. It could be 100 degrees outside. How far will you
be able to walk with the sun beating down on you at that temperature? It could be 5 degrees. How far could you get in that type of chill?
Get in the gym. Go running. Do something. I stay in shape, for myself, but I know it would never hurt if I got into a jam. Hope for the best,
prepare for the worst.
Aside from fitness, buy a tent. Any tent will due, but if you have money to spend, buy one that you won't have to replace after a few uses (i.e; not
Wal-mart). You can always build your own shelter, but chances are, if you're reading this you probably don't have that know-how.
Buy a backpack to carry that tent. Buy some basic accessories. Stock up on matches. Buy a good pair of hiking boots and extra socks. Make sure you
have clothes that will keep you warm but fluid in the winter, and clothes that will keep you cool in the summer.
Educate yourself on survival techniques. Learn how to make fire without a lighter or matches. Learn how to create a shelter. Learn how to find a
food source, be it plants or animals.
Create a plan. Know where you're going to go and how you will get there. Don't just set off wandering, you could find yourself in even more
IF this were to happen, only the strong will survive, and you can bet there will be stronger than you out there. Arm yourself, somehow. Just about
everyone has a gun. Should you get one? That's your call, but some sort of defense mechanism will be needed at some point...