I'm a long time DC area resident (since ummmh, 1966), and have been more or less trapped by DC winter weather four times. Once for 12 or so hours, once overnight (I walked into a motel and asked for a room---and got it!)

The key thing I see missing is a down (or some modern fiber filled) sleeping bag. I see you have the liners, but don't know how warm they will keep you on a really bad night. You may need to stay in your car a long time. Your preps seem fine for a few hours, but you need to sleep also. And I worry that you might be too cold with what you have. A warm sleeping bag and protection from wind/cold/rain/snow in the car can make things much more comfortable. (note: I do not trust "warmers" to work when you need them.)

In all instances, it was NOT the ability of my car or me to deal with the snow and ice on the road. It was the total stoppage of all traffic on the road (I495 ((aka the Beltway)), Rt. 7 in Virginia, I270 in Maryland and 16th Street in DC) that stopped me.

So, my philosophy is be prepared to sleep in your car, totally passive (no external heat), and be comfortable and safe ---doors locked, and stay warm in good quality sleeping bag.