When flying cross country, I find it harder and harder to get direct flights and with tight connections, sometimes grabbing something in the airport isn't viable so I generally end up packing myself a lunch and some snacks. There are lots of things you can pack if you are a little creative -

1. Sandwiches - these are a no brainer - pack the lettuce an tomato and condiments separate (and yes, those condiments go in the liquids bag but I always find I have room for them).
2. hummus - it goes in the baggie as well, but a small container doesn't take much room - i bring some pita bread, cucumbers, carrots, a piece of fruit and a granola bar.
3. Salads - kale, brussel sprouts and any "slaw" type salad works great - stick with an oil and vinegar dressing - I add in nuts, dried fruit, etc. etc. These will hold for a pretty long time. Pack in a small disposable plastic container. Grain salads (couscous, quinoa, etc.) and pasta salads are also good choices as they don't get soggy.For ideas, check out Whole Foods - they have a lot of these types of salads for inspiration. If you need to keep something cold, freeze grapes to use as a cold pack!
Instant soups/oatmeal that come in those cardboard containers. Sprouts and Whole Foods generally have a pretty good selection and some of them are fairly tasty. You generally can get hot water (for tea) on the plane. Just add it to the container and bring a spoon!
Individual packets of almond butter (goes in the baggie too, but those packets are pretty flat) crackers, Babybel cheese, string cheese, nuts, small tangerines/oranges and bananas are also good choices.

I travel carry on only and put my lunch/snacks in my "personal bag".