Why bother with all that, just carry your cell phone and AAA card jeez guys its the 21st century, you don't need all that repair gear for offroading, just a phone and your roadside recovery card.
I mean that's what you guys go all out to say to people when they say they want a bare bones truck without all the electronic nannies, you should apply the same principle to your offroading expeditions, also don't bring first aid kits just call 911
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I don't really go that far offroad anymore so I don't carry much. Never carried anything when I had my 96 Jeep Grand Cherokee, never needed to do any repairs out on the trails. With my Bronco 2 I don't carry much other than extra oil and coolant. I do have an extra fan belt which for some reason works on the alternator or the power steering pump. I figured the 1 belt would be sufficient to at least get me back home. I don't need AC or power steering, but having a fan that spins and an alternator that alternates is far more important LOL. I carry the stock spare tire, and a good jack with a few boards to throw under the jack and block the wheels. If I recall my old 12V air compressor is in the box as well as a generic SAE/Metric socket set and a few wrenches and screwdrivers. Threw extra hose clamps and radiator hose and heater hose.
As far as major repairs you may as well get hauled to a shop because if you are offroading in deep snow/mud/sand, etc. you ain't doing a transmission swap, driveshaft U-Joint repairs, etc. in that crap. At least carry the tools to remove the offending driveshaft though so you can at least with help of another vehicle get off the trail. Other than that I wouldn't carry too much excess stuff, it just adds unnecessary weight and takes up what little space we do have to carry stuff, not to mention crap that's going to go flying out of the vehicle if you roll it so no need to pack the vehicle full of stuff you'll just have to spend hours picking up later when things go south, and the way some of you guys go flying down trails unless you can secure it all very well it becomes projectiles in wrecks, rollovers, and other emergencies.
If you are venturing out a first aid kit, shovel, fire starting equipment, toilet paper, generic hand tools, good jack, lug wrench, extra lug nuts, spare wheel studs, possibly a spare brake hardware kit, plugs to shove in leaking brake lines, duct tape, electrical tape, wire connector assortment, spare belts, spare hoses, extra locking hubs, u-joints, ignition coil, spark plugs, plug wires, distributor cap & rotor, some sort of pad to lay on while performing work under your vehicle, extra fluids, tire chains, recovery gear (winch, come-a-long, tow strap, traction mats--floor mats will work in a pinch too), flashlight with good batteries (doesn't do any good if the batteries are dead), emergency beacon so you can be found, probably won't have cell phone service so having an emergency beacon/tracker is a great thing to have and have it so you can reach it in an emergency not buried in a box somewhere that you may not be able to get to after your truck flips over on a trail and you are stuck hanging upside down in it. Communications gear (2 way radio, CB, Ham Radio, GMRS, etc)...that fancy cell phone of yours probably won't do much good in the middle of nowhere, or after your truck has flipped over and the phone went flying to a different universe. A whistle to signal for help, water, food that is easily prepared or that requires no preparation, maps of the area you are in, alternate routes pre-planned, tell people where you are going, how long you'll be gone, and what routes you plan on taking.