Any & every pastry! Well, there may be some that don't qualify, but most we've had are 1 snack credit: including those extra large ooey-gooey cinnamon rolls (Main Street Bakery/Magic Kingdom, as well as some resort counter service) Sweet pretzels and school bread from the Kringla Bakeri/Norway/Epcot, apple turnovers, blueberry muffins, choc chip muffins, choc chip croissants from Main Street Bakery/MK and resort counter service.
At POFQ, they had biscuits & gravy for $3.49...a snack credit. And we like the fresh, hot beignets there too.
Another thing we have for breakfast sometimes -- at many of the park counter service restaurants, the desserts are pre-packaged & portable. Especially if we're getting a large lunch we'll choose a more "breakfasty" kind of dessert -- like the carrot cake option so many CS carry. We pop them in the backpack, then refrigerate overnight for a yummy breakfast (have also done that with chocolate cake...a nice little indulgence for vacation

)
Editted to add--we almost always leave parks mid-day to go back to hotel room for a break/nap/swim. So we find that it's very easy to stop at a park bakery on the way out & use snack credits to buy the next day's breakfast (that way we just carry it right out of the park back to the hotel, instead of carrying it around all day/night. Also, if you wait until end of the night, they'll be out of a lot of choices.) And this way, we have a quick breakfast ready in the hotel room -- no getting up early to go get breakfast, and no standing in line, waiting for breakfast first thing in the park. But if you're thinking you might do this, take several extra-large ziplock bags. The to-go pastries will be packed in a standard to-go box which is not airtight...your pastries will stay fresh overnight if you put the to-go box in the large zipper bags once you get back to your room.