The in-park options tend to be pretty sparse. Most of the resort QS have decent hot breakfasts.
In MK, a BOG ADR gets you a QS breakfast. You can also get a breakfast sandwich and coffee at Main Street Bakery. Otherwise, it's mostly snack credits: Sleepy Hollow has a snack credit waffle. Gaston's has snack credit cinnamon rolls. The market in Liberty Square has some stuff. Auntie Gravity's has smoothies.
Epcot, Sunshine Seasons is again serving breakfast. The bakery in France has pastries. There's the Starbucks for sandwich-coffee.
HS... uh, Starbucks. Starring Rolls should have some snack credits?
AK: Starbucks, again.
Disney Springs: Wolfgang Puck Express.