I almost always fly American, so these are generally restaurants in AA concourses. I would love it if other AA fliers posted their recommendations, too. I have considered making this thread for years, so I'm glad to see it bumped.
ORD breakfast: Frontera at H/K is great but can be quite slow, especially when busy. It's also pretty messy, so leave enough time to wash you hands afterwards. Their napkins might as well be notebook paper.
ORD lunch/dinner: Publican Tavern. Very close to the security/exit at the H/K concourse. Absolutely outstanding peri peri turkey avocado sandwich. Fries are almost always perfectly crispy. I would eat this meal in non-airport contexts once or twice a month if I could. If another traveler is sitting near me and I can tell that they don't know what to order, I will offer the unsolicited suggestion that they order this unless they don't like spicy food. I can't recommend this sandwich enough.
SFO: Starbird - Nashville chicken (non-spicy chicken also available). Bourbon Pub - Crab Louis salad.
PHL: Chickie & Pete's - both traditional and unconventional (lobster, etc.) cheesesteaks. Miscellaneous crab stuff.
LGA: Soleil Brasserie (on a mezzanine level slightly above gates) - lobster roll. Good, but small. Order two if your clients footing the expense account won't mind. Friendly bartender. Also Hunt & Fish Grill - chicken BLT is often quite good, but very occasionally meh.
MIA: La Carreta (Cuban - better than Versailles, but after having lived in Miami for a decade, I find the whole Versailles thing - and most of the people who go there - to be quite irritating...).
LAX: Everything sucks. Cole's (allegedly invented the French Dip at the non-airport location) has been going downhill, but it used to be good, and I'd say that it still sucks the least, relative to your limited options. The spicy mustard is outstanding. There's a female bartender who is always so grumpy and short-tempered that it's entertaining, so sit at the bar.
CLT: I'm a sucker for Bojangles, partly because I don't live near one. Cajun chicken biscuit. Try it with honey. But it's just fast food.
I probably have plenty of other recommendations, but these are the ones that truly stand out in my mind without having to think about it.