I've started riding a lot of the converted rail trials like your C&O in DC. Just starting out with a trailer, kids seat and two kids I can ride an easy 10mph, 15 if I push a little bit. So if I had to some of those are alternate routs.

Sure 4x4 doesn't help evacuating a city by road, where it helps is if you need to hop a curb or U turn in the highway berm, the police are not very nice to you if your stuck in the middle of the berm

Communications are another essential, scanner and/or CB, you want to hear where the accidents are stopped traffic is.
Good maps, GPS, etc. You want street maps, bike trail maps, etc so you can plan alternate routes.