Imagine if your car simply ran, without adding fuel or charging it?

I don’t think this will happen, but boats are different, because they are on water, and water can become hydrogen.

Combining two forms of sustainable energy into one range-extending propulsion system, Swiss Sustainable Yachts’ clean, quiet catamaran promises to jumpstart a future in which the word “range” becomes obsolete. The 64-footer harnesses solar energy to create its own hydrogen, powering a fuel cell-electric drive to potentially limitless autonomy, so long as the sun is shining and the captain isn’t pushing past cruising speed. 
https://newatlas.com/marine/aquon-one-solar-hydrogen-yacht/

The article goes on to say:

The idea of relying on sunlight to create electricity, to power hydrogen conversion, to again create electricity for propulsion sounds rather inefficient on its face, and we have doubts as to whether the Aquon One will be able to produce hydrogen as effectively as billed or obtain anything near “limitless” range. 

I tend to agree but what if it is better?

We already have solar-powered boats but this could be next level.

If it does work, and of course efficiencies can be improved, how can this be used on land?

We could park our cars in a lake… Or of course use tap water. So instead of going to a charging station for our hydrogen, we can make it ourselves. That isn’t autonomous though. So here’s an idea – canals. Maybe just to replace trucks, but with the added benefit of delivering water to places that need it in our warming world.