We only purchase breakfast 2-3 per trip (we usually stay 10-12 nights) so that is a lot of breakfast in the room.
I usually buy milk from the resort store. I pack some cold cereal, oatmeal, trail mix, dry roasted peanuts, granola bars, small jar peanut butter (for peanut butter "spoons"), flavor blasted goldfish, and a few of the individual bags of Funyuns and Cheetos. We also save our juice and desserts, including pudding, applesauce, and fresh fruit to take back to the room.
In general I expect that we eat the cereal, oatmeal, granola or fruit for breakfast and the other things for snacks. However, ds's favorite "Disney Breakfast" memory was the time he ate a bag of Cheetos and a resort mug filled with Cherry Coke on the way to the bus stop. (I ate the funyuns!).
At home whenever he wants to eat something crazy for breakfast he asks for a "Disney World Breakfast" - basically at Disney anything goes!