General advice: (there's been a bit of this already in the thread, but I'll restate some of it based upon what I do in preparation)
1) Snacks/food and something to drink. I keep a pair of MREs, couple bottled waters, and a couple packs of Lance snack crackers in my truck all the time. Should I ever get badly stuck, I'll be relatively comfortable.
2) Change of clothes: I keep a small duffel tucked behind my front seats with a complete change of clothes along with 2 or 3 pairs of socks. I've dug into this kit a number of times for dry socks or a dry shirt or something. I also keep an old set of hiking boots with the clothes.
3) Flashlight with spare batteries... get a good one, something waterproof! (I have a 3-D maglight and a 2 AA maglight in the truck all the time).
4) Shovel. I prefer a spade or at the worst a "coal" shovel. Plastic snowshovels work great for loose snow, but if you have to dig into the snowbank you're stuck in, they arn't gonna work a hoot.
5) Blanket and/or a heavy beach towel. I tend to keep a blanket and a towel in the truck (I've used the towel for drying off when I've gotten caught in the rain an soaked to the skin along with it's intended use. It's also better than nothing for helping keep you warm if you get stranded. I keep a "space blanket" in the truck as well.
6) Among other things I also often keep a small power inverter in my truck with a cellphone charger. I got a big enough inverter that will also power my laptop if I happen to have that with me. And often have a book tucked in somewhere. Stuff to help keep me amused while I wait, if I'd have to wait. I also keep maps, compass, matches, lighter, sturdy knife, first aid kit, and other such items with me as well. And a set of jumper cables, good ones about 12' long.
From my adventures driving a 2wd Ranger....
I usually can't do the trick of filling the bed with snow because I'm always hauling tools and such around with me. And because of always hauling stuff around, I need as much bed space as possible. I've tried having bags or buckets of sand, gravel, or rock salt, but they always take up too much space and if it's a bucket, it's gotta be secured. I've ripped bags open by accident trying to load stuff and was always trying to keep them covered to protect them. Then I hit on a solution... bags of lead shot. They're small (about 6"x10"x1.5") and weigh 25lbs a piece. And they don't move. I throw a couple around each wheelwell, usually in front of or behind, thus leaving the middle of the bed open for gear.
Tires make a big difference. I've tried street tires. I've tried mud tires. I've tried aggressive AT tires. I've tried in different situations too. Street tires bring the suck as far as I'm concerned. Mud tires work GREAT in deep snow or freshly fallen snow as long as it's more than an inch or two, but suck when it's hardpack or ice (especially if you have muds on all four corners). Then I tried a set of Sport King ATs in the winter, an aggressive siped all-terrain. They worked great on hardpack as long as you were easy with the skinny pedal, better than any of the muds I've used. They worked well in deep snow too. Ice they were passable, they worked better than muds for sure.
That said, a set of V-bar chains over muds ruled all. They're a miserable one to get worked on an properly tightened over a set of muds, but will make a 2wd with an open diff act like a tank, I've plowed through snow that went up over the top of my front bumper like that. Oh, yea, less weight is better with mud tires... I only ran about 150 lbs max with muds, usually closer to a hundred or less. The ATs worked good around 250-350lbs.
I pretty much always keep my chains in my truck when winter hits. They can make even junk summer treads work good in snow, they bite MUCH better than studs on ice. But you don't want to run them on dry roads and they don't like speeds over 35mph. FYI, if you're stuck and can't move enough to put the chains on, you can jack up the tire and put the chains on.