The whole point of a plastic petrol can is to keep a little bit of spare petrol in in case you break down?? FiL said it's dangerous and combustible (surely so is the petrol in the tank?!) and the point of the can is to carry to the petrol station if you break down. Why would I do that when I could just buy an empty container at the station?
AIBU? We got stranded on the motorway oncecwhen DH didn't fill up the car. Not good times dressed in heels etc for a wedding.