Cheese and Crackers
Here, one must keep in mind the first rule of airplane snacking: first, do no harm. OK, that's someone else's rule, but it applies here too. If you are some kind of cheese snob, this is really not the time to bust out the Limburger. Your Camembert, your Stilton, your Vieux Boulogne should all be left at home to be enjoyed in better-ventilated environs. To avoid a mid-air incident, it's best to stick with the milder varieties -- think Colby, or maybe cheddar. Individually packaged string cheese is also a great option.
Not what you would call super healthy, cheese is basically made of artery-clogging fat, but, you know, it's cheese, so it gets a pass -- for reasons of sheer deliciousness. If you're really concerned about it, stick to low-fat varieties and whole grain crackers.