Cereal in the sense of "contains lots of rolled oats", no Kelloggs-type stuff has ever supported me long enough. No high-sugar commercial granola mix. I add yoghurt instead of milk.

I like a soft boiled egg, and some bread and cheese works too (although all you USAnians are, sadly, bread-and-cheese-challenged in the eyes of this Swiss miss....)

On the road, I take only water. I hate the sticky feeling in the mouth and the thread somewhere about caries is exactly what I suspected would happen from sipping highly sweetened drinks during a whole day.