Without reading the other replies yet I'm gonna say a flare gun and a bottle of bourbon. Even if you're stranded you need to stay in the holiday spirit, that's why you need the flares.
I have a rain jacket (the regular kind not a condom) with a hood, flashlight, basic toolkit (pliers, screwdrivers), blanket, and I have a weather radio somewhere in there. I keep forgetting to put another bottle of water in there. Gotta have a chaser.

