I use the Betterlife Back Support Belt for travelling which supports the spinal and abdominal muscles but gives some movement. It's no miracle cure for back pain but I think stops your back from moving around when you are travelling be it in the car, plane or train.
I did get a few funny looks at security when the buzzer went off and she had to check me over!! This is not the only one this company sells, they have a number of different types. The company also has lots of disability aids and other products which can help make your holidays more comfortable.