My #1 recommendation would be on board air for airing down, and airing up, re-seating beads, etc. A 20lb beverage CO2 tanks are common among us snow wheelers and jeepers, because they are fast, high pressure/volume and can reseat a bead, and run air tools for about a minute or two. A compressor would be adequate too but they aren't as high volume, many guys have both

Then a SOLID set of recovery points front and rear.

After that you can start putting together a good recovery gear set and put it in a large bag or one of those rubbermaid action packers.

At a minimum:
*Jumper cables- self-explanatory
*Full size spare and jack Hi-lift is fine, just be wary of them, and if you're gonna use a hilift do yourself a favor and get sliders.
*Basic Hand tools
*Some sort of shovel- For the snow the folding e-tool ones work well because you can fold it like a hoe, and move massive amounts of snow fast. They're compact and don't take up much space
*3-4 quantity 3/4" screw pin shackles.-I like the Van Beest green pin ones but it's not a big deal here they are all pretty much the same.
*Kinetic Recovery Rope- Having used both the ARB style strap and the rope, I would say the rope style has an advantage in terms of how violent the recovery is. But they are both better than a traditional nylon  strap, which has no place in a recovery kit. It is possible to get a good 20mph rip on one of these ropes and hardly even feel it, which is why solid recovery points are a requirement. Masterpull Superyanker, Viking Offroad , Bubba rope, etc. They are all pretty much the same, I would recommend the 7/8" ones which will cover mid-size suv's and some of the smaller fullsize trucks. But I'd reccommend going bigger if you are gonna be playing with some of the bigger trucks or diesels.

*Reliable means of communication for the area you will be in - Cellphone, CB, VHF, etc
*Warm clothes and a sleeping bag- if you're gonna be out in the boonies by yourself
*Some extra food and water just in case Couple cans of chili or spaghettios is how I usually roll
*Some way to start a fire Some cars have a test port with a schrader valve on the fuel rail, soaking it in paper or pouring it over some sort of kindling/tinder. Jumper cables can be used as an ignition source but a lighter is usually easier.

Winch?:
 *Synthetic rope - It's less dangerous and easier to work with, it doesn't store energy like steel and if it breaks it doesn't cause carnage, and you can also tie it in a knot or splice it unlike cable
 *Tree strap of some sort- I said I don't like the arb kinetic strap as much as the ropes for recoveries, but I prefer their treestraps because they fold up compact and take up less space and I can put it under my seat,etc.
 *Snatch block- That suits the type of rope or cable you are using- For synthetic this is the nicest snatch block I've seen so far: http://www.masterpull.com/snatch-block-sbo30000/
 *Winch extensions - 80-100 feet or so, of the same strength as your main winch line. What I do is make them out of my old rope when its time to retire it, since the extensions are not used as often its ok, but you could also buy new or buy some amsteel blue and splice it yourself for way cheaper.
 *My thoughts on pullpalls,maxtrax, etc- Waste of space since you are usually out with other people that you can recover off of. The pull pall does not work well in all environments (it is useless in deep snow), and by the time you get the maxtraxx out most people are already buried up to the frame rails. I WOULD however give them extra consideration if you are doing a lot of solo adventures or overland type stuff where you don't have other vehicles to support you.

Extras:
 *TOILET PAPER OR BABY WIPES- You never know when you're gonna have an emergency
 *Set of goretex's- USGI surplus ones that you don't give a fuck if they get trashed are fine
 *Gaiters -if you're gonna be in the snow/mud etc
 *Chains?-I don't own a set of chains because they are counter productive to my 4psi wheeling style but if you are going to be in the snow or ice and don't have lockers, or aren't an experienced wheeler they wont hurt to have in case.