We used to keep a couple of short length of rail on the tenders. The 480's had a couple of hooks on the tank frame to hang a short length of rail. I think the 490's lacked the hooks, so the rails went up on top of the tank.
They were useful in rerailing if a truck got slewed in the wrong direction or to get the wheels closer to the rails if they had wandered to far astray. Spike one down at an angle ahead of the offending wheel and it will get forced in the right direction. Once it gets back close to the rails, set the frogs, and hump it back on the track.
I did this 3 times in one day with the Hinman(burg).