First, you need one that runs when you need it too. Your bug-out vehicle cannot be covered with a tarp inside of a barn somewhere waiting on the apocalypse. You need to know what it is capable of doing under various road conditions, so it has to be driven, tested, and maintained. Even those vehicles not driven much will need their fluids changed to keep rubber seals and gaskets lubricated to prevent drying out and shrinkage. Belts and hoses will need to be inspected and replaced as needed as well.
You will need more than a working knowledge of the mechanics of your vehicle, so repairs can be made by you. For starters, you need to know how to change the oil and filter, air filters, tires, transmission fluid/filter, and you must know how to replace all belts and hoses.
You probably do not need a vehicle that looks like it was in a Mad Max movie. Bells and whistles while impressive only means more maintenance, so unless a gadget or accessory enhances your survival prospects do without it.
Four wheel drive is a given, because off road driving is very likely in a grid down scenario. You will need to move around obstacles, and other vehicles along the highways, so this means off road driving. The vehicle’s clearance has to be high enough so you can navigate over rocks, logs and other low lying obstacles, otherwise you will have to blaze a trail the entire way by moving things out of the way.
Cargo space, most SUV’s have some, but it is not likely to be enough room for supplies for an extended period for you and the family. A trailer is an ideal addition to your vehicle, but there are downfalls, because a trailer means more maintenance and expense when it comes to tires, lighting and so on.
However a closed trailer provides protection from the elements for your supplies, and of course allows you to carry much more in the way of supplies and equipment, and it can be used as an emergency shelter as well. Even an open bed trailer can be used as a shelter by stringing tarps, because the bed of the trailer gets you off the ground. Therefore, you should have a vehicle that is capable of pulling a trailer.
You may not be considering a trailer right now, but things change so make sure your vehicle has the hitch capability whether you think you need it or not. In a crisis you may come upon a trailer, so you have to be prepared to take advantage of certain situations as they arise.
A mounted winch would be the best case scenario, but if this is not possible then at least have come-alongs (cable pullers) of adequate size. Having one too small for the job is the same as not having one at all so make sure you size it correctly.
For most people, their BOV would be used to get out of a dangerous environment to a safer environment. You cannot just jump into your vehicle and drive aimlessly for days however. You need a destination and the fuel capacity to get there, and then move locations possibly, and ultimately get back home.
How far can you go on one tank of fuel. You need to know, and then factor in that you may have to backtrack, move around obstacles, and possibly even circumvent large bodies of water. You need to have multiple routes mapped out, and know how many miles it is to your final destination when using any of the routes. You need to know so you can stockpile enough fuel.
Fuel is heavy and you cannot just toss it in the backseat with the children. Without fuel you would have to abandon your BOV and probably much of the supplies you are carrying. Again a trailer is an ideal addition, because you could easily carry enough fuel in or on the trailer.
Hauling a trailer will make off road driving more difficult, but there are tradeoffs with everything you do, so you have to weigh the pros and cons of having one versus not having one.
Your cargo space can be increased with roof cargo boxes or rails that can be used to tie down supplies and equipment. Some of your cargo room will be taken up by bug-out-bags, tools for repairs and spare parts/materials such as batteries, tires, oil, antifreeze, and so forth.
Your objective is to move from one place to another with as little problem as possible. Any vehicle you have could be a BOV, but if you have a choice then choose wisely, by considering among other things, maintenance, cargo space, off road capability and can you and your family shelter and eat inside the vehicle when needed.