Fuel cans and functional gas stations:
In conquest, using a conquest-optimized vehicle (meaning it is very very cheap) will usually result in it having a few liters of gasoline leading to it running out of gas fast. I think adding a purchasable gas can tool that refills any kind of fuel (meaning it'd have to be expensive or there would be many types for each fuel type) into the vehicle.
Gas stations should also have this ability like the garages have the ability to spawn vehicles, and fuel should also be at the garages as well.