A lot of people are starting to consider the concept of "bugging out" in times of natural, civil, economic or other disaster, preferably to somewhere else they know rather than just "on the road".
Usually the recommended vehicle is a tricked out 4x4 but a few people consider bicycles for obvious reasons (freedom from fuel reliance and the ability to get past obstacles and traffic jams)
You could see in Japan after the Tsunami that the first vehicles in use by surviving locals were their faithful granny bikes.

What would you want in a bug out bike. Most of the recommendations are by people who are not particularly bike buffs and they tend to be a bit low end for my liking, eg discount store MTBs. I would aim for a midrange hybrid/MTB or a Surly style practical bike or in the UK, something by On-One.
Personally I see the ideal vehicle as one that also serves as a daily commuter and tourer with dynamo lights, hub or derailleur gears, rear rack with front rack capability, possibly front basket. I would also fit a trailer hitch even if I didn't carry a trailer. You can always find ways of making trailers fit a non compatible hitch.