There are tank stations , if they were functionable, so you would have a fuel content which decreases while driving and there is a need to fuel it up every amount of fuel you want or full. And car mechanics to repair your car if it is damaged. This could be part of a story mode, so you need to earn money to get your next full tank, repairing your car or buying new car parts like different shock asorber or different, maybe even self-made varnishing or just a completely new car. Even without story mode fueling your car up is always nice, it adds more deepness to the game! Also the car mechanics! One extra: If the fuel tank is damaged, it can loose fuel, which you can also see on the fuel display.
the decrease in fuel already happens same with the damaged fuel tank. this has been a topic nearly a thousand times since the games birth
While the game maps are too small and most people dont drive enough to notice, the fuel amounts and efficiency in the cars is realistically handled, and reset each time you reset your car, so if you drive a little bit then reset each crash you will never notice that the fuel amount does go down. In fact, if you've looked into scenarios, there are quite a few related to driving cars low on fuel.
But reloading fuel is not possible, also there is no car mechanic. especially this was the main part of my suggestion.
Refueling is in game, just scenario only for some reason. I believe a dev said there are no plans to implement it in freeroam unfortunately. It certainly would be nice though.
If that's the case then its a major mistake, there's fuel stations in every map and there's fuel consumption that even gets worse as you increase the power of a car. To not have refueling in the final game is an oversight.
Personally I'd just like to see it as one more thing to make free roam feel more developed. Currently the WCUSA drag race is basically the only thing we can interact with on any map.