I have questions like how does he get gas if it runs out?

Mail vans can travel 450 miles (or 700km) on a single tank. Since a horse drawn cart would take 5 days at ~5km/h for 8h per day that’s = 200km already. That a very conservative estimate with all the other driving going on, so I would say by the latest chapter he is a bit under half a tank left (or around 300kms) as for if the guy runs out of fuel? I’d say his car is pretty much unusable
But hey that’s just a theory, a fuel theory

Bro, that's amazing.