Assume that a hydrogen fusion power generator is developed sometime in the future, the goal of massive research programs.
Assume that smaller and smaller fusion power generators are developed over time.
So there will be fusion power generators that can fit into gigantic super ships, or maybe even smaller ships, And maybe spaceships, and maybe locomotives, and maybe cars, and maybe airplanes.
And maybe those fusion power generators will power electric motors to drive those vehicles.
Or maybe those fusion power generators will power fuel production plants which make chemical fuel for engines for the vehicle. Vehicles operating on Earth could take water, or water vapor in the air, and use electricity to split it into hydrogen and oxygen, and store the hydrogen and oxygen. And when enough is stored up the vehicle will be able to burn the hydrogen and oxygen, producing water vapor and energy to power motors such as internal combustion engines or steam turbines. If the water vapor is saved it can be split into hydrogen and oxygen over and over again.
And any decent sized tank of hydrogen for the fusion generator would contain enough hydrogen to last for years, decades, centuries, or millennia.
So whether this type of vehicle used the power of the fusion generator to power electric motors, or used it to produce hydrogen and oxygen to fuel chemical motors, it couldn't operate eternally but could be made self contained as far as fuel sources were concerned for years, decades, centuries, or millennia, assuming there were no mechanical problems.