My preference would be for a kit to make me comfortable while waiting in the car, not while leaving the car. Sleeping bag, adequate clothing, a little food, signalling devices (cellphone, mirror, whistle, etc.), some way to generate a little heat - maybe one of those moveable wick Nuwick candles (used with appropriate ventilation of course). The chances of me deciding to leave the car to wander off into the snow are about zilch. I don't put myself into deserted areas far from civilization in the middle of winter. Some people have to, and then I think it would be good to have gear for both scenarios: stay-with-car and leave-car. I still think the most prudent choice the vast majority of the time would be stay-with-car though.

Most of the stuff in your kit would be perfectly appropriate for a stay-with-car scenario too. I would add a sleeping bag, an insulating pad, and a tarp & paracord for additional shelter. Duct tape would be good for covering windows broken in an accident, etc.