I always like to take the single serve round cheeses for in the park snacking. It provides protein, carbs, and a little fat to help us until we get to the next meal.
We take the little cheeses to the parks, too, but there's no carb in cheese… just protein and fat, unless you are eating a cheese blend (like a dip or spread, or sometimes very cheap processed slices will have a carb filler) or have some crackers with it. Still, these cheeses provide a great shot of protein during the day- we love 'em!
We always take breakfast foods with us- things like mini-bagels, peanut butter, cereal, cream cheese. I freeze yogurt, juice boxes, capri suns to use as ice packs for the cream cheese. Everything goes in a suitcase. We also bring our small, 4 cup coffeemaker, well wrapped, and the mini-moos creamers (or just buy half-n-half at the resort, along with milk for the cereal). I like the idea of freezing muffins and will probably add that to my list. Breakfast is not a big deal for us; we'd rather each do our own thing and eat as we dress rather than spend park time at a food court breakfast.
For park snacks: Granola bars WITHOUT chocolate/pb chips (they melt), gummy fruit snacks, fruit roll-ups, baby bel cheeses, cheese sticks, graham crackers (I take them in a storage box). Not too much fruit as apples and bananas bruise, but tangerines (halos or cuties) were very popular last time- but bring a baggie for the peels!
We usually fly Southwest so it's no biggie to dedicate a suitcase to food. If we are on a legacy carrier, I try to justify the cost of a checked bag by what it'd cost us to have breakfast in the food courts. Of course, then we all have to pack our clothes in our carry-ons and backpacks, as I am NOT paying for TWO checked bags!