Literally, anything. I've seem to find that a lot of cultures don't actually place an emphasis on having a specific food for "breakfast." Ideally, I'd eat something light when I wake up like some fruit or something and then a couple hours after I wake up I'd eat something a bit more fulfilling. But most of the time I roll out of bed and rush off to work having eaten nothing at all.
I'm a bit surprised to see yogurt listed here, because that seems like a really good choice for a breakfast food. Especially slightly sweetened and with a bit of fruit on top, yum.