Each park has at least one place open for CS breakfast, however none of them IMHO are great uses of CS credits. Main Street Bakery at the MK has a breakfast sandwich of some sort, Tuskers at AK has a decent counter service breakfast, The Electric Umbrella is open at Epcot as are some places in the Sunshine Seasons at the Land in Epcot. I am not sure what is open at the Studios, but I am sure someone will know.