I would also add a few of those chemical hand warmers, and a hat. a lot of body heat is radiated from the head.

Of course, I carry all that stuff (except I do jeans, and don't do the ski stuff). I also carry at least one sleeping bag (rated to -60),
TWO highway safety kits (full of first aid stuff, flares, etc)
two shovels (you don't think I'm gonna dig you out on my own, do you?)l
a battery powered lantern,
three flashlights,
2 gallons of water,
a spotlight,
a ton of spare batteries for everything that requires batteries,
two books (if I do get stuck, having something to read would be good),
two cellphones (though I pass one off to the next Mission Coordinater at the end of this month),
three two-way radios, (2 VHF, one 800MHZ - the 400 will be going in this weekend, I hope)
a snatch-strap,
emergency blankets (mylar),
my mars light
and a bundle of 'empty' tags (tie 'em to the door handle/antenna, lets the next searcher know that the vehicle has been checked and was empty)

And I *never* travel anywhere without my Emergency Response Guidebook (a book dealing with HazMat rules - lets you know what's (supposed to be) inside that truck, based on the plackards on the outside) Order your copy at 800.327.6868 or www.jjkeller.com.
Rule of thumb. If you roll up on an accident involving a truck (particularly a tanker or UPS) stay far enough back/upwind/uphill that you can cover the whole scene with your thumb. Let the blue canaries go in first.

edit: I forgot to mention - that's in my POV. The 4x4 has even more cool stuff