maybe while on the bus, you could use that opportunity to develop other aspects of awareness. Sometimes, when I am in that situation, I just observe my mind, as in where is it at?
Keeping your eyes open and senses alert (that way you won't miss your stop), just observe whatever enters and leaves your consciousness; the movement of the bus, people entering and leaving, your inner reactions to the people around you, the passing scenery...and, of course, the breath if you like, but really when on the bus it's better to practise a form of awareness that keeps you alert to what the current task is. The one thing I watch out for is daydreaming. If we just get bored and daydream, then we really are wasting time. But if we somehow remain alert, even just to our state of mind or the passing thoughts in the mind, then we have cultivated awareness, even if just a little it all adds up over time. You could even daydream mindfully, where you observe yourself drifting from thought to thought. It's all good - so long as you reaming awake and alert!
all just my personal opinion and based on experience. not gospel.