Here's the good news about this strategy: The bus driver will never know. The bus is too big to rock when you jump on, and the rearview mirror can never catch you. The bad news is that you need to hold on tight as hell if you don't want to fall off. If you fall you're either going to get hit by another car, or you're going to roll on the ground for a while. Neither seems like a great outcome, even if it does save you a couple bucks on the bus fare.
I actually know the story here. This guy had gotten into an altercation on the bus which got him kicked off. Unfortunately his bags were still on the bus, so he grabbed on and stayed with his bags in the only way he knew how. Someone hire this man. He'll do anything to get the job done.