Travelling with your cat
Cats are territorial animals. They have spent ages establishing their territory, and they guard their 'turf' as fiercely as any teenage hoodlum. From a cat's viewpoint the world is divided into such territories, each 'owned' by someone who will do as they would with an intruder on their territory. This means that a cat outside his home patch is a nervous cat who expects retribution for trespassing to come down on his neck at any moment. This is why a cat in a new environment will either hide somewhere safe and defensible, complain bitterly to its humans, or (in the worse case) head off home. An average cat explores an area not greater than three miles, and will expect that 'home' lies within this area, since as far as he is concerned the world is not that much bigger.
It also does not help that planes, trains and taxis are outside a cat's normal experience, and that when travel does happen it usually ends up at the vet - which most cats do not consider a positive experience. So expect your cat to hate travelling, and to be unhappy once you reach your destination. That said, there is a lot that you can do to make the experience less traumatic for both yourself and your cat.
It is very important that you get your cat a good travelling carrier. A cardboard box with holes punched into it will not do for anything but the most temporary container, and will give you a surprising demonstration of how effectively a hysterical cat can burrow through apparently solid surfaces. And the last thing you want is an escaped cat ricocheting around your car on the motorway or bounding about the airport.
Before you choose the container, consider the psychology of your cat - and remember that it is highly advisable to get one container per cat. Some cats like the all-round view from a wire cage where they can see potential threats from any direction. Others prefer the security of a covered container, with a small panel to peek out of. If you are not sure, take your cat on a test run in a wire cage, and see if covering most of it with a towel helps to calm the cat. Make sure that you can add and remove things from the container without the cat launching itself from within like a feline ICBM. Remember, an insecure cat is a cat with highly active bowels and bladder, and you will not be popular with your fellow travellers if you don't have the means to remove the source of the small PDQ (pretty damn quickly). For the same reason you will want to line the bottom of the cage with absorbent material, and check that it does not leak. Note also that if you are transporting the cat by plane, the airline might have its own ideas of what cat carrier you should, or even must, use.
If the cat is going to be imprisoned in a container and taken into an unfamiliar (and therefore in the cat's terms, hostile) environment, you should at least make sure that the container is itself a known quality. It is worth getting the container well before any trip, and leaving cat treats inside the open container where the cat can find them. Take the cat for a few short journeys in the carrier, making sure that nothing exciting happens en route. Make sure that the cat's favourite toys and blanket go into the container with it. There are pherenome sprays that are said to reduce tension - you might want to experiment with these. The container does not have to be particularly large - an insecure cat will probably prefer an enclosed space, but make sure that the cat has a good air supply and can stay warm.
On the journey
(Aeroplanes are a larger and more complex topic - we will deal with that septely)
Some cats like the view from the window - most don't. In any case, do not let the cat out of his carrier; not least because in a car he might decide that under your feet with the pedals is the best place to be. Wherever you place the cat carrier, make sure that it is secure. If you have to brake suddenly, a cat carrier hitting the back of your head at 30 or more miles an hour will do little to improve the travel experience for either yourself or the cat within. Try not to use the boot (trunk) of the car - it can overheat, it is dark, and the airflow is poor. On a train you can carry the cat on your lap and talk to it in an attempt to keep it calm. For some reason, when your cat miaows, you will get particularly indignant looks from mothers with the same infant kids that scream like banshees throughout all other journeys.
You will want to supply some water, and your vet will tell you where to find water containers that do not spill easily. Food on the other hand is unlikely to be eaten, and anything eaten just before the trip may be vomited up during the journey, so give the cat a few good meals well beforehand, and then nothing for the final 5-6 hours before you set out.
You can certainly expect the cat to complain lustily for part or all of the trip. This is a sign of unease rather than physical distress - your cat is explaining that it does not like the current situation, and is quite prepared to spread the misery. If you are lucky it will eventually accept its fate and perhaps even settle down for a snooze. Remember if parking your car at a rest stop, to do so somewhere where the car will stay cool. Heatstroke can kill a cat, and at the least will add to the stress and misery of the journey. Before the trip you may have considered giving the cat tranquilizers. By the end of the journey, you may feel that the pair of you need them. However, if you do decide that your cat needs doping, check with the vet - some cats actually become more excitable after 'tranquilizers'. Never give the cat pills that are meant for humans. And remember also that tranquilizing the cat during the journey might make it harder for it to recover from the trip afterward.
The information supplied here is intended as a guideline only.