Range will be most important and good highway milage won't help much when your stuck in the stop and go traffic jams while trying to bug out. Most cars, while having great highway milage don't get much better stop and go milage than a 4x4 and usually have smaller gas tanks.
You may need to hop a curve or drive onto the median to get around an accident or stalled/out of gas vehilce. You also may be involved in minor fender benders as road rage goes to an all time high and you want a frame based vehilce instead of a unibody for those situations.
Past history shows that bugging out means you will be sitting in traffic for a long time, you want a good sized fuel tank and good battery and starter so you can shut off the engine and sit for a while and a vehilce that can idle for long periods of time. Getting stuck for hours on I70 in the middle of summer when the PA road departmnet decided to shut down a lane out front wheel drive minivan would slowly overheat even without running the A/C. My 4x4 truck I can sit with the A/C on full blast for as long as I have fuel with no problems overheating.