Portaging a kayak
On a trail, the kayak can be carried on a yoke. Two homemade styles are shown below.
They are described here: http://www.qsl.net/ws8g/kaybackrack.htm
On a road or hard surface, a cart can be used. It may be a small cart that fits under the kayak,
Or it may be a set of wheels as part of the kayak.
When moving longer distances, moving the kayak with a vehicle is convenient. Roof racks are an obvious choice. Another way to transport the kayak by vehicle, is to build or buy a kayak trailer. In addition to the type shown in the photo link bleow, there are also some pretty neat kayak trailers that use motorcycle tires and are quite light and affordable.
Rack or Trailer?
The choice of rack or trailer is an interesting one. With the price of complete roof racks from the big companies going through the roof, a trailer is not necessarily a significantly more expensive proposition, especially if you are moving several paddlers around. Roof racks put the kayaks up high - especially if you drive a truck. That can make loading and unloading a pain. With the kayaks on the roof, aerodynamic drag is somewhat higher and fuel economy suffers. It's not unusual to see 20% or more increases in fuel consumption. Trailers, by riding in the vehicles slipstream, do increase drag but by a lesser degree. With today's fuel prices, you can save a lot of money on fuel with a trailer. That might not make up the price difference between a rack and a trailer, but it can come close for some.
Trailers do suffer in other ways. They increase the length of your vehicle and you have to learn how to handle parking and backing up with a trailer. As well, you will incur higher costs on some ferries and toll highways or bridges. At home, you need to have space to store the trailer when not in use. There may be licensing costs as well. Finding appropriate parking at the put in can be a pain too.
With a roof rack, you are limited to the design load for the combination of rack and vehicle that you have. In some cases, that is not strong enough for two sea kayaks. As well, all your gear is going into the vehicle - some gear could go into the kayak on the rack, but only to the load limit of the rack. Some trailers, on the other hand, can carry four sea kayaks comfortably and have a box on the bottom to carry some, if not all, of your gear. As such, four sea kayakers with all gear can fit into a minivan or mid-sized car with a trailer. Commercially available roof racks realistically limit you to two sea kayakers at most.
Wes Boyd also has some useful comments on kayak trailers at http://www.kayakplace.com/gearboat/trailer.htm.
Travel by Train
In Canada, the passenger rail companies still provide a service that is almost as old as rail intself. If you are a passenger on the train, you can carry your canoe or sea kayak in the baggage car for a small additional fee. In some cases, you can also arrange for a drop in the wilderness and a pickup at a later time. Getting to and from the train is your problem and you can only go where the train goes, but this is one option that paddlers still use. The downside, of course, is that if you are travelling a significant distance (as in from one coast to the other), the price of the passenger ticket is quite high compared to, say, flying. However, it is the most civilized way to travel and your ticket basically includes travel and accomodations. You can get up and walk around and sit in a dining car to eat. There's even a bar car for evening get-togethers. If you, like me, have romantic notions about rail, train travel is a viable option to get to a distant kayak destination with your own kayak in comfort - if you have the time and money to enjoy it.
If you need to transport a kayak across the country and you are not driving there:
Contact a shipping company or shipping broker. Many transport trucks have spare capacity and can carry a kayak in addition to their regular load. This will be cheaper that trying to ship a kayak directly.