Geez, mate, that scenario is an old grizzly with a sore tooth, and you're asking us how to take its temperature (non-oral thermometer) and come back alive.

Well, maybe that's overstating it a bit.

200 miles is the worst-case scenario, but it's do-able for seasoned backpackers. If it's primarily on established roads, you can cover a good distance each day -- provided you have adequate food and footwear.

You'll probably have to carry extra water in places, unless you are very sure there's accessible water ahead. That adds to your pack weight, and reduces distance travelled per day.

Aside from standard backpacking gear, a few things come to mind.

- Information is going to be hard to come by, but if there is a radio station still transmitting in the area you'll want a small radio to tune in. Same with a cell phone -- if you can get a text out to let family know you're okay, that will relieve a great deal of worry.

- A portable solar option to charge spare batteries for lights and other items may be worthwhile.

- Any quake strong enough to take out tunnels will leave the mountainsides extremely unstable. You may need to cross a landslide or work around it. Some rock scrambling gear and the skill to use it might be a worthwhile option.

(Outside of the parameters posed, though, I have to say that if you are in a relatively stable zone with your vehicle and gear, I think the only real option is to stay put. Someone will be along in due course. Unless there's a town with a pub and air conditioning just over the rise ...)