It's not particularly surprising, but the fact of the matter is there's nothing to improve on a piece of fruit. An apple or a banana will quell the hunger, and they come in their own convenient carrying case. Apples have no fat, no sodium, no cholesterol, and they're high in fiber and potassium. The humble banana also contains fiber, and even more potassium, not to start a banana vs. apple fight here.
Oranges can be a little messy for close-quarters plane consumption, but again they're highly nutritious providing lots of fiber, potassium and more than 100 percent of the recommended daily allowance of vitamin C [source: USDA Nutrition Database]. And don't forget bite-sized options like seedless grapes, blueberries and raspberries.
One word of caution on flying with fresh fruit -- inside the continental U.S., you should be fine, but crossing international borders, you may run into import restrictions, so if you bring it, eat it or dispose of it before you get off the plane.