About a decade ago I have a vivid recollection of spending a three-hour sit scouring the ATL airport for a banana or apple. No such luck.
But things are better now, most airports will have some healthier offerings... your odds and options will be better west of DEN.
You can also pack fruits and veggies, I do that to supplement whatever I can find on the road. Pretty much avoid fast food like the plague now.
Some folks elaborately pack all of their main meals for a four-day, or all of their food period. It can be done, but it's a bridge too far for me personally. I prefer sit-down meals, too many MREs back in the day I guess. These days I view airline trips as an extension of my life which should be more enjoyable than not, as opposed to just a mission to gut out to the end.