In general, the most common point of failure is...
-Front axle u-joints. I would suggest carrying the tools and perhaps some spare parts to fix this. The U-joint in the JK Rubicon is different than the common 297X joint so I would carry spares. The JK does use 'captive' unit-bearings in front however, so if you do ruin the front axles you can pull the axle out and drive without it. I would suggest plugging the axle tube to keep the gear oil in, or pull the front drive shaft if you don't have those parts. I would suggest buying a print version of the factory FSM and using that for your tool reference AND keep it in the Jeep at all times.
Most of the other breakdowns are going to be slightly more common and should require more common tools and spare parts. I would suggest....
-The oil pan on the 3.8 JK is aluminum. I would suggest a skidplate or an upgraded steel oil pan. The transmission pan if its an automatic can also use some help.
-Radiator hose repair tape. If you don't have a working cooling system your not going to go far. You can carry spare hoses but they take up more space. A hole in the radiator can can crimped off well enough to get you back to civilization.
-Engine serpentine belt. This runs the entire engine accessory package....ie alternator, power steering pump, and water pump. I would suggest a spare and the tools to change it.
-I would suggest a few quarts of engine oil and ATF. If you where to develop a slow leak this can get you home. If you get a big leak and you find a way to patch it you will need some fluids to put back in. Engine oil can be used in a differential in a pinch, but I wouldn't suggest highway speeds! ATF can be used in the power steering system in a pinch also.
-I also highly recommend using Lube-Locker reuseable gaskets whenever possible. They are pretty affordable and easy to use. Its REALLY nice not to have to worry about having a spare gasket or making something when doing a trail repair.
As far as tools go, I would suggest looking in the FSM and breaking down what repairs you might be likely to make. Don't carry the world. Carry the tools you need and some 'universal' tools that can work if needed.
