I would echo Samuel's caution about bringing expensive cameras and lenses along for a cab ride on a coal-burner. The environment is not very friendly to electronics and glass. I have brought DSLRs, but I typically keep it as small as possible, so I can protect it physically, in a small case, when not shooting. That means removing battery grips and using a wide prime lens (20mm) instead of a zoom. Most types of zoom lenses are "air pumpers" and they can bring dust into the body of your camera. A coal-burner cab is a VERY dusty environment, and that dust is also very corrosive. Get that stuff inside the body of your camera and it will eventually destroy it, not to mention covering your sensor with abrasive dust. Don't even THINK about changing lenses in the cab. A friend of mine destroyed a Canon 5DM2 by changing lenses in the cab of a NG coal-burner.
Now, if you're riding in the cab of an oil-burner.....never mind! Oil-burners are a much cleaner ride. I still recommend going small and simple. Bring a small case to physically protect your camera when not shooting.
/Kevin Madore