I was talking to a coworker and I mentioned that in NYC, in a mass evacuation, with about 24 hours of warning, the best way to get the hell out of the city would be by dirt bike, followed by motorcycle, then bicycle (preferably a cross bike). Anything else would be stuck in traffic for more than 24 hours when you suddenly try to evacuate a city of 10 million.
Granted some people have family and possessions to take along. If I had to make a checklist of stuff, it would be:
2 water bottles, a small water filter, batteries, radio, handheld CB, a 9mm, extra ammo, bag of balance bars, extra change of clothing, reflective mylar blanket, first aid kit, small tool kit, fire starter, high volume hand pump + co2, my 2 DVD+RW's of backup data, all my ID and cash, cell phone + charger, and sunglasses, easily fits into a backpack.
I can't see anything else that I would need considering I only need to get about 100 miles away, anything more and we're talking apocalyptic war of the worlds type destruction.