For a few long weekend trips I have done this.....
pack a small electric kettle, instant oatmeal/grits/cream of wheat, individual fruit cups (pears, peaches, applesauce), instant coffee/tea bags/cocoa mix (and shelf stable creamer and sugar, if needed), disposable paper bowls and plastic spoons, paper coffee cups (with lids) and paper napkins. I have also packed homemade FROZEN muffins (in ziptop bags or vacuum sealed). I can get all of this, except the kettle, into a shoe box.
Then the first one up starts the kettle, then one showers while the other(s) eat, etc. Even the TINIEST rooms at the value resorts have a small table and chairs. We use the table as our "kitchenette" and neatly store everything on it so that the maids don't have to clean around our stuff (and so we aren't making any more work for the maid).
We have been able to have an inexpensive, relatively healthy, FAST breakfast with very little effort (and no long walk to the food court). And the disposable cups with the lids insures that we can take our drink along for the ride to the parks if we don't finish it. I used to include juice boxes when the kids were smaller, but they aren't needed now.... but are certainly an option!
The biggest drawback to this is the need to check a piece of luggage (partially because of the liquids and partially because of the extra space it takes up).... but the extra space in the suitcase on the return trip home is for the souvenirs, right???!!
You could also consider things that others have mentioned like granola bars, bagels, peanut butter, etc. Anything shelf-stable that can be made/eaten with a minimal of time and equipment and is still relatively healthy would be fair game in my mind!
Just be DOUBLE SURE to keep the kettle unplugged when not in use! Have a great trip!.................P
ETA: Yup, I am one of those "take a photo of everything" kind of people! Here is our breakfast set-up from this past May. It looks like I used a small priority mail box this time around. DD had two homemade (healthy) blueberry muffins (that obviously got a bit squished) and I had instant oatmeal, fruit, and a (previously frozen) Vitamuffin. Plus coffeee/cocoa for each of us. The M&M tube isn't for breakfast.... it's the coins for the pressed penny machines!