If you're going to take your own vehicle to give you maximum flexibility in your travels then the complications of organising your trip increase many fold. The cost of taking your own vehicle may not be that much more than using public transport in the developed world but may be many times that of public transport in the developing world. The added flexibility and capability to go anywhere makes up for the extra expense. The more people that travel in one vehicle the more cost effective it will be.
This is obviously firstly limited to your budget and also the kind of trip you're going on. Two wheels may be preferable to 4 although it does limit how much gear and spares you can carry. If four wheels the most important thing is the terrain your going to travel in. If you're off round Europe anything will do and the old beaten up VW camper may be perfect. For further a field and travel in the developing world a four-wheel drive may be a better option. There are several things that need to be borne in mind when choosing a vehicle.
The paper work required to get a vehicle across a border can be quite involved and remember that at each border there will be paper work to fill in as you enter and leave a country. Therefore don't bother trying to cross a border in the evening, try and get there first thing in the morning to allow plenty of time. Remember to dress smartly, comb your hair and that the officials are 'always right'. You vehicle may get searched so organise it before you get to the border remembering to chuck out any contraband that may be illegal in the country you're leaving or arriving in. It's very easy to forget that bottle of scotch, but it could cause you serious problems if you're trying to enter a country where alcohol is banned. If your just travelling around Europe then the paperwork is minimal but further afield things get more complicated paperwork you may need is listed below. If you want to find out more information check out the world database on this site.
Driving Licence You will probably need an international driving licence or driving permit. The former should be obtained before you leave home the later may only be obtainable upon entering the country.
Carnet de Passage Normally referred to as a carnet and obtained from your countries main motoring association. This is basically an insurance policy or bond that you show at the border if you then fail to export the car out of the country again you will have defaulted on the carnet and the country will claim the required taxes from the motoring association. You will end up paying the money if you do default on the policy. If you have a serious break down or crash and can't export the vehicle then it is important that you obtain proof. Photographs and an official letter from the local police should be obtained and forwarded to the relevant authorities.
Insurance If possible try and get this sorted before leaving home if cover is not available for the countries you are heading to then it may be available at the border or in a neighbouring country this obviously needs to be checked before leaving. In some of countries in the developing world motorbikes do not need insurance and in some you may find car insurance isn't required it is advisable to take out policies anyway if possible in case the worst happens.
International Certificate for Motor Vehicles If you home country registration document is not valid in the countries to be visited then you'll need one of these.