I have done many expeditions to different countries. Including a trip to Ushuaia in Argentina which is the southernest point in the world. Some have been expeditions that have taken over a month. Although, I have a TJ that is very capable I dont use it for this type of expeditions.
I have a 2005 80 Series Land Cruiser. (yes they still manufacture them in S.A.) There are some essential things that can be adapted to any vehicle to make for a fine expedition rig.
Here is my list of most important things.
-Double gas tank. Even though Jerry cans are great, and every vehicle should at least carry one, they are heavy and are usually mounted in high places (roof, tire carrier, etc..) and weight is the most important factor on expedition vehicles. You definetely need to keep a low center of gravity plus you can fill up the main time while rolling forcing less needs to stop. Time and schedule are usually tight on this type of trips.
-Double battery (preferably gel cycled) with a perco style switch and not an isolator. When isolators fail it usually takes a toll on the alternator.
-Power inverter of at least 1500 watts, paired with low amp draw bulbs to make camp light.
-Roof top tents are the way to keep you safe from wild life.
-The most important thing for me are full floating axles. These will keep you going if there is a failure on the axle.
-Tire size is key for long travel. On the 80 we travel with 285/70r16 (33x11) and its also recomended that is there is a convoy you all have the same tire brand and size. At one instance we had a truck flip over and destroyed 3 tires. If all of our spares werent the same we would have been stuck for a while. Not everywhere is tow truck friendly, most of the times you are on your own.
-I dont trust any winch that is not warn! PERIOD!!!
-Important spare parts: Driveshaft, axles, power steering hoses, alternator, radiator sealants, U JOINTS. fuses (yes really), air filters, and at least one oil filter and oil.
-Suspension, Used many of them nothing takes a beating like Old man emu. We had all kind of issues with suspension, just imagine busting a rear shock and then having to drive your truck with all that weight without damping....not cool or safe. Also, OME can be suited to fit the amount of weight expected on the vehicle, keeping the truck stable and not saggin.
-Emergency kit, pure oxigen tank and a person with a valid course in first aid (you get these at the red cross). Lots of canned food and drinking water.
-Good tool set, hilift jacks, chain saw and hatchet
These are basic things I have learned with experience, there is a lot more to an expedition vehicle.
Here are a couple of pics of recent trips.