DFW is my home airport and I worked there in college so I know not just the terminals but remember many of the nooks, crannies, and side roads around the field. Suspect many are gone with all the remodels but can certainly find my around pretty confidently.
As a college kid pushing wheelchairs, the AA cafeteria was great, especially if you got there about 9pm as they were closing down. They had a nacho plate on the menu and at closing you would get pretty much all the taco meat that was left as well as all the toppings you wanted.
Best place for a sack lunch was a service road that ran just off the ends of the west side runways. You could sit there a couple 100ft off 18R and feel the turbulence as the airplanes went over, a great place for spotters. If I remember correctly you turned where the AA maintenance hangers are and it took you into the employee parking area. Looks like it is gone now, I know it was closed to the public around the time of the Gulf War.
If you are traveling through and have time between flights, Pappadeaux’s for Cajun food (Terminal C, it is below the concourse in an old TrAAin station) and Cousin’s BBQ in Terminal D are my favorites. Whataburger opened out there a couple of years ago in the Terminal E satellite which is a bit of a hike but worth the trip if you have time.
When I was travelling regularly I could find my way around LAX, IAD, ORD, PDX, PHX, SEA, PHL, STL, ATL and numerous small airports. I’ve walked the entirety of BOS and PHL as I had plenty of time to connect from a Barbie jet terminal over to the mainlines so just hoofed it.
Restaurants across the airports have all gotten the same, though I do like grabbing a dog at Gold Coast in Chicago or seafood in Seattle. Otherwise anyplace I could sit comfortably and get good internet and power was a good spot.
Only airport I found annoying was MCO (Orlando) and that was mostly due to the elite status types bringing their families through the high speed security line and clogging it up.