Vehicles
Wow this one is wide open. How do you want to prepare vehicle wise... I'll leave vehicle contents for other discussions. This will focus on the vehicle itself and what's needed to support it.
Being from the north, the first thing I think about is snow. Is my vehicle ready for snow. I guess that would lead me to what I would figure as a first consideration. Where do you live, which I suppose is coupled to the question, in my peraparation scenarios, where do I want to be prepared to be? If you live where there's snow, it's probably not a great idea to have a primary winter vehicle that isn't 4wd or AWD. If you live in a climate that doesn't have rain and your preparation scenarios have you in an enviroment with at least dirt roads, maybe a 2wd vehicle is ok for you. I'm not going to talk about whether you live on an island or so far in the bush that a plane is necessary...
So Climate is the first consideration. With climate comes a couple of other questions, what's the minimum temp you'd expect in your scenarios? Whats the max temp? Bottom line is your vehicle equiped to manage those extremes. If you live in the north where it gets subzero regularly, is your vehicle set up for cold weather starting?
Do you want to have one vehicle year round? or do you want a winter rig and a summer rig? Do you want to prepare to the point of having a fully dedicated bugout rig? It's up to you...
Some starter thoughts
Up North standard stuff:
4WD- If you live where there's a reasonable expectation of snow, a 4wd or alwd is best.
Tires- Slick tires don't do much for you, use an all terrain/all season tire or get set up with a winter tire rotation.
Starting Temp - Do you have a garage? someplace to keep it warm? If you want it to "always" start, that's a great thing to have. Otherwise a block heater is probably a good thing. It's probably a good thing to have a block heater anyway.
Windshield Washer Fluid - Use the low temp stuff in winter
Window heaters - get them if you can.
Starting Power - I always go with the biggest/ largest, highest quality, most Cold Cranking Amps (CCA) I can get in the battery size that fitts the vehicle. The colder it is, the more your going to dig into those extra CCAs.
Phantom Draws - This could be in any catagory, but is especially important in cold environments. If you have little gadgets you leave plugged in, or leave an accessory like a dome light turned on, over a period of time when the vehicle isn't running, you will drain the battery. This may prevent you from starting when needed. Keep track of these things. If you serously want something that will start every time... Put a dead man switch in. That will ensure nothing is pulling power when the switch is off.
AC Power - If you can, get a vehicle that has an integrated AC inverter to be able to run 120VAC (or whatever your countries native voltage is) items. At least 150W or so. Enough to run a computer or charger or air compressor or the like. If you don't have one, highly consider getting an aftermarket one.
Grill Cover - Some folks use grill covers when it's cold to retain heat in the engine and cab. Certainly makes sense in the below freezing conditions.
Kit - I said I wouldn't talk about contents, but I will just a little. Keep a shovel, tow strap, cold weather rations, and clothes at least...
Fluids - Keep in mind that fluids used in machinery depend on the ambient temp much of the time. This really used to be the case with vehicles running 10w40 vs 10w30. Very similar but one had less viscosity and was better for cold temps. Seems most vehicles run in the 5w30 range today. Either way, check out your vehicles manuals and use the recommended fluids for the areas you intend to be.
Universal Considerations:
Discression - It's up to you how blingy you want to make your vehicle. Much philosophy in the prepping world suggests its usually a good tactic to blend in. Will you blend in if you have large stickers on the side of your vehicle that say "MY BUGOUT RIG", no it'll probably make you a target for folks that think you have some extra goods. It's probably good to have a normalish looking rig for most people. But do what you like. It's hard to make a Unimog look like a Camry... just sayin.
Defense against the dark arts - Are you the president? do you want to be protected like the president? This will be a short section, but obviously your prepping can end up with you owning a bulletproof rig with oil slicks, escape smoke, quarts of spare blood etc... how extreme you want to go is up to you. We're gonna stop short of that level for now.
Ping, I need help - Does your vehicle have onstar? Do you have a spot beacon? Your cell phone is great for 95% of the issues you might encounter, but consider having a service like onstart from GM or getting a satellite based communicator like a Spot Beacon to txt for help if you're in a land of low signal.
Maintenace Plan - You have 40 gallons of rice packed away to keep you going but don't have an extra quart of oil for your rig. Some things to think about.
Keep it running - At any moment in time you might be relying on your vehicle for a 1500 mile trip, getting away from the rona, getting to your ailing parent, evacuating from a chemical fire. Never know.... Treat your rig like it's a tool that always needs to be ready for use. Get it fixed when there's problems, better yet have a vehicle you can do your own maintenance on and keep it up.
Critical Spares - Do you need to keep a full extra transmission? Maybe, maybe not... oil? definitely, windshield washer fluid? for sure. Spare tire? Yup.... What else would make sense to keep as spares. think about it, do some research on you particular rig. make some decisions. Many vehicles are very dependable today. There are probably some spares you could consider though. Spark Plugs, maybe a coil pack or two, hose clamps and a few feet of different size universal hose, one changeouts worth of all of the fluids, spare tire, air cleaner, some universal battery ends, fuses, wiper blades, maybe a set of brake pads and rotors...
Availability of parts - I knew a guy who drove a geo metro. He had 3 extra geo metros of the same style out back that he could rob parts from. Probably a great plan if you can stomach some extra vehicles sitting out back. Does it make sense to drive a 1972 rolls royce? it might if you've got the means to keep it running. It seems to me it's probably best to have a mainstream manufactured vehicle that's maybe up to 20 years old, preferably one that's common to your area. I'm pretty sure I can get almost any part for a 2010 silverado where I live. Probably not for that Unimog though.
Hot Weather
Samesees as Up North - Probably the up north list is a good place to start, but dial down on the cold weather gear, shovels, block heater, etc.
AC - I don't know how folks survived in the heat without AC. I'm calling it a necessity. Get it and keep it working.
The right are - did you change out the air in you tires? did you put the winter air in? It's kind of really a thing. If you put 40psi of air in a tire at 90 deg f and you drive to wi in the winter, you won't have 40psi when you get there, don't worry it'll come back when you get home. The volume of air contracts as it cools, as such you might only have 30psi in your tires when you get to WI. Soo the short version is keep an eye on tire pressures as you go through different climates and keep tires inflated to recommended pressures,.
Coolers coolers coolers - Most vehicles run around 200F. If the ambient temp is 110F, the vehicle will have a harder time dissipating the heat from the engine, thats why it's vitally important to make sure you cooling system is working properly. Keep up on that maintenance. If you're hardcore, you might consider a larger aftermarket radiator or adding a transmission cooler if you don't have one.
Tires - Winter tires are made for lower temps. their going to be more pliable in low temps. At extreme temps they may be very pliable and may wear very rapidly, you might only get 10,000 miles in the hot weather.
You ready for a breakdown? - You're in the middle of the desert, it's 110 with no one in site. how do you deal with it. Area you ready for a breakdown like this? I'm from the north so there are many people more experienced, I'd think step one is water and step 2 is shade. Do you have water in your rig and something that can be used as a tarp?