I would have to strongly disagree that "buckets" are the best way to transport large fish. First of all, my 24" royal clown knife would have a hell of a time fitting in a bucket that has a diameter of 11" at it's widest point.
Second of all, the surface area of a bucket doesn't alow for adequate gas exchange with a surface area of only about 95 square inches, whereas an ice chest offers a surface area of around 288 square inches if the ice chest was 2ft x 1ft. Like I said before, fish are shipped internationally in bags and boxes. When was the last time you saw one delivered to a LFS in a five gallon bucket? Ice chests are a great way to go, and so are rubberbands totes are great to if ambient temperature will allow their use, but the downside to transporting them in these is that water will inevitably slosh around and get whatever vehicle you are moving them into get wet. When I bagged and moved my fish, I got the opportunity to put them in the cab of my truck and reap the benefits of having a climate controlled cabin to house them.