The best breakfast-on-the-run spots we've found open at early entry at Epcot is Fountainview Cafe (including chocolate croissants, muffins, bagels, danishes, juice, milk and better than usual coffee selection).
At early entry at the other parks we usually head to:
MK - Main Street Bakery
AK - Kusafiri Coffee Shop and Bakery
MGM - Starring Rolls Bakery.
Have fun!