Watch where the flight crews go. Often they’ll bypass the overpriced places with big lines and go to the hole-in-the wall cafe that you might otherwise walk right by. I’ve done this a couple times with good results, mostly for the purpose of avoiding long lines.

The actual answer here could not be simpler,

Just use the food review web sites – they very much cover airports just as they cover cities.

https://www.eater.com/airport-dining-guides

https://www.yelp.com/biz/one-flew-south-atlanta

https://www.yelp.com/biz/ecco-atlanta-2

For any airport, you can google

"Best place to eat, XYZ airport, terminal 3"

or

"Fine dining airport XYZ"

or

"Localvore demeter organic eating Amsterdam airport"

and you will find a tremendous host of both consumer-written and pro reviews and articles. Bon appetit.

Depending on the rest of your travel plans, taking part of a meal with you can be a good idea. A salad and fruit, for example, don’t (have to) need refrigerating and can be eaten in waiting-area seats either with a sandwich bought at the airport, or before/after one of the smaller (lighter/better value) options from an eat-in place.

This is a good option at your departure airport or when changing flights not far from the start. It’s less useful if you have a long leg followed by a short one, and carrying fresh produce can be problematic at some borders. I’ve been known to take almost a picnic with me, only buying drinks at the airport – at the time it was Burger King or an overpriced sandwich worse than I could make, so that was an extreme case.

Some big airports in Europe have supermarkets in which you can buy a salad or there are secctions with warm food like chicken, pasta… and sushi as well.

If not, then I prepare something at home easy to eat, like a quiche or a tupper with pasta salad and I take some fruit.

Some airports have staff canteens. The one I know for sure is Singapore. Travelers are allowed to use it if they can find it (just ask an employee). The food is both cheap and delicious, since it’s intended for the residents (who are used to amazing food in the rest of the country) and not expensive and bland like in the passenger restaurants. I believe it is still cash-only though.

(jpatokal’s comment mentions a link providing directions and photos: singapore – Is there a hawker stall selling local food in walking distance from Changi airport? – Travel Stack Exchange)

Some airports have clubs. The last one I used was “Club Mobay” in Montego Bay. For a reasonable fee you get to use their lounge while waiting for your flight, and food and drinks are free. (It’s also available for arrivals, giving you priority service through immigration, but unless you are in a hurry perhaps not as worth it as at departure time.)

A random one-off food concession in an airport, agreed, can be pretty “hit and miss”. So you see “St Louis Bread Co.”, what the heck is that?

However food chains should have comparable quality to any of their restaurants. So McDonalds at BWI should be just like McDonalds in Streator, Illinois. This is greatly complicated by a couple of trends.

• The sharp trend toward “Fast Casual”, such as Panera Bread, Chipotle, Mod Pizza, Five Guys, Potbelly’s, etc. Just as they’re becoming the desired thing in trendy malls, they are very much the desired thing in airports too. Is a Mod Pizza at the airport as good as a Mod Pizza anywhere? You bet. Many are perfectly wonderful. The problem is in hearing about them. I had no idea Mod Pizza existed until last year.

• Shops who are perfectly competent at running chains, but stay in one city. So Uno’s Pizza in Chicago, Leo’s Coney Island in Detroit, etc. The problem is, you haven’t heard of them.

• What I might call “artisanal fast casual”. These are quick-lunch-accessible eateries who are local beloved institutions, but are small operations. Some airports are insisting on shops like these instead of Burger King or even Five Guys. With the SFO remodel, they begged them to open an airport location, as a matter of regional pride: for many, the airport was only their second location. So at SFO, you’ll encounter shops like Buckhorn, Ebisu Sushi, Bistro Burger, some beloved Mission Street burrito vendor. These make locals go “hurrah, good food!” But of course, as a non-local you’ve never heard of any of them. So you can’t distinguish them from some lousy airport vendor.

The upshot is, you have to do your research.

Many of them (hats off to Potbellys, and Leo’s Coney Island in DTW North), have quasi-normal pricing despite the airport location. However that can feel like a pinch if they’re in a naturally expensive market like SFO.

TL;DR: Overpriced businesses prey on travellers who are in a hurry and can’t shop around. These people probably will think, once in a while, why not pay $3 for a small bottle of water? To save money, you will need to know the airport and its surroundings to find decent stuff/fairly priced stuff. I assume the rule applies to every airport. My example is Düsseldorf.

Example: In the case of an airport that I know well, Düsseldorf International Airport, DUS, you pay premium prices in the the security area. If you go to the main hall, it’s still somehow overpriced, but not outrageous. OR you can go down to the basement and there there’s a supermarket, some normal bakeries and smaller no-name restaurants.

The cheapest option inside the airport is to buy some ready-to-eat stuff in the supermarket.

If you wanted to pay even less you can take the SkyTrain, a fully automatic cabin railway, which is for free, and go the train station. There the prices are completely in the normal range.

Some airports may have apps that allow you to have food delivered to you from other terminals.

As an example, San Diego International Airport has two terminals, 1 and 2. Terminal 1 is a very crappy terminal with three separate secure zones, and each one is very small and offers very little choice for food, while Terminal 2 is a very modern terminal with tons of dining choices (including the best Thai food I’ve ever tasted).

The airport offers an app called “AtYourGate” which allows one to order food from any restaurant in the entire airport and have it delivered to any location within the airport in any terminal. I often use it when I have a flight leaving from Terminal 1, as I find the dining options in all of the concourses to be mediocre and crowded.

The app ordinarily charges a $3 delivery fee, but I frequently find the delivery workers handing out promotion codes for free delivery. There is also an airport employee discount you can claim in the app, so you can follow the advice in Nean Der Thal’s answer and ask an employee to pick up your order for you and show their ID (because the delivery people have to verify it when someone claims the discount in the app).

There must be similar apps offered for other airports, and even this particular app seems to have aspirations of expanding into other airports.

Most airports have their own websites: perhaps they have info on food. For example, SFO had a nav link, which had a “Dining” link, containing brief descriptions and the names of the places: https://www.flysfo.com/shop-dine-relax/dining/

You could take a name that looks promising and check for a review of it on something like TripAdvisor. Or maybe the restaurant itself also has a website with a menu and prices.

Depending on airport and airline, you may be able to buy yourself into an executive lounge for a nominal fee, even as an economy passenger. Some airports sell day passes into lounges.

This will give you access to a more comfortable waiting area and better food/drink/service.

Price and availability does change, but it’s an option worth investigating. I was offered my last one by the check-in staff.

One time I found a decent place serving tasty food to taxi drivers at Toronto’s airport (a short walk outside to where the limo drivers park). They’re mostly South Asian, so the place had good basic oily “sweets shops” type Indian fare like thali, nan and so on. Of course once you go through security you lose that option.

Similarly, years ago, when I frequented Taipei’s airport I found a “secret” cafeteria that served up excellent basic Chinese food to the workers at a fraction of a price of the big (usually empty) restaurants.

To find that kind of venue, you’d have to ask someone (they might not tell you) or do some in-depth research of the particular airport.

Not sure if either is still there, both were more than 10 years ago. I don’t eat that much these days, and if I do anything I usually just bring a few security-compatible snacks in my carry-on. Gorp, chips (crisps), fresh or dried fruit, jerky, that sort of thing. Sometimes apples, instant oatmeal and powdered 3-in-1 coffee for arrival so I don’t have to go searching when I get there. If it’s an international flight with customs at the destination you can consume anything in-flight that might cause them to raise their eyebrows (especially meats). Most of the flights I take these days have edible meals so I don’t need to worry about being hungry after the doors close.

Many airports these days have food from well-known chains (albeit at higher prices, usually) so it’s not so much an unknown as it once was. Not so much better, but predictable. I’d rather plan out a place once I arrive (if the time is suitable), rarely is anything at an airport very memorable.

If online resources aren’t doing the job as you said, then the only logical solution is to find an employee who seems to be friendly, and ask them!

Employees know better, perhaps they even know some secret places that allow passengers to buy from. If they are super nice, they can offer to buy you the meal (using your money) using their discount (many airport food places offer employee discounts), I did that myself (as an employee).

I’d find an empty counter with an employee doing nothing and ask them, or ask the cleaning staff.

I have the same problem, and the only solution I found is to buy food ahead of the trip and take it with me – you can buy several subs, for example, and take them through security before your first flight, together with one or more empty water bottles. You would only need to refill the water bottle somewhere inside the secure area, or buy other liquids, if you don’t want water.