Definitely been discussed before.

To MissJoeyDFW's comprehensive list, I'd add:
* Poached chicken, cut into bite-sized pieces, tossed with a light sauce (but not something that could be construed as a liquid...a couple tablespoons of chutney or tomato sauce, for example, but nothing that spoils at room temp). I refrigerate after preparing & put in a ziplock bag + carry a disposable fork. It's usually still cold/room temp by the time I eat.
* Sushi
* High-protein bars
* Beef or turkey jerky

I would NOT bring vacuum packed/canned tuna on a plane (or any cooked fish). I think it's too fishy smelling.

If you're flying internationally, remember that you may not be permitted to bring leftovers into the country, particularly meat or produce products. I recently bought a package of jerky in Chicago, carried it with me on a trip to Africa (never opened), returned to the US & had to deal with Customs inspectors who were very cautious about letting me bring it back into the country. (Had I thought about it before boarding the plane home, I simply would have tossed it.) Many a traveler has gotten themselves in hot water for tucking a piece of fruit from their plane meal into their carry on, saving it to eat later & then forgetting about it until it's discovered at Customs.