I usually pick up something I can put in my back pack that will last through a bike ride and a bus ride. So something that doesn't spoil and doesn't make massive messes. I like breakfast bars, oatmeal bar things (more like squares), cereal (dry), fruit (depends on my back pack load), and such things. And if I'm lucky I can get hot tea/coffee to fit in my water bottle holder in a to-go container. If not then bottled water.
If its available. By the time I would get to eat the yoghurt its like warmish and kinda gross. And dairy in the morning makes my throat kinda gunky feeling.
I hear much about this love of marmite...not sure if I'd find it too salty - though I like branston pickle on a cheddar sandwich, so maybe I'll try some marmite some time.