The US doesn't have the same landing fee system many places the rest of the world uses (Australia, New Zealand, Great Britan, etc.) so most mom and pop places don't charge an initial landing fee at small airports.
Using an FBO (Fixed Base Operator, gas station, airplane parking Lot and service provider all in one) at busier airports (and even some small ones) you will be charged a Handling or Ramp fee based usually on your airplanes weight. This can be waived with a certain amount of fuel purchased or other factors.
Many small FBOs have self serve fuel, which is billed at a lower rate than having a line service worker fuel your airplane for you. If an FBO does not have a ramp fee it's good practice to purchase "courtesy fuel" to help them stay in business. Fuel is often the best source of revenue for these small businesses which are disappearing at a rather alarming rate. This is usually what's practical. For a small airplane (Cessna 172) you might purchase 10-20 gallons. I did and try to. Only one time in a piston airplane [Mooney] was I ever limited by weight (we were returning to home with one more pax than we started with) to not buy any fuel from an FBO that did the following free of charge:
-Hangared the airplane for the approaching thunderstorm and accompanying hail.
-Provided a car to take to lunch free of charge.
-Restocked my fancy cooler for the passengers with extra sodas and waters. I had the beer covered
I asked them to bill me a hangar fee for the trip since I used their services and they refused. This was Indy Executive (KTYQ) at Montgomery Aviation and I'd never had a bad experience there. This was a regular stop for us and I showed up the next time with plenty of room in the tanks for gas
I'm shutting up now...
Be sure to tip your line guys
