I did when I lived in Germany, it’s a legal requirement, then for a few years in the uk, till the kids came on the scene, ran out space!
Not sure this is true. I lived there for 10 years and even took an HGV test there in the 1990s, never heard of such a thing.
Anyway back on topic, always had a can in the back of the Landy because you never knew if the gauge was working properly and those things are a pig to push even to the side of the road and boy were they thirsty, also those days if you did run out you had to manually bleed the air out the system with a spanner at the roadside if you did run it dry.
The habit continued as I live fairly rural and there is always the possibility of an "Ooops forgot to fill the car again" moment.
This year I bought a much newer car and a few reasonably priced petrol stations have opened on some of my most travelled routes. ( Remember when the rural stations used to cost an arm a leg and a kidney for half a tank?)
Haven't really decided if I need a can in the back but I have one in the shed just in case I ever make up my mind.
At some point someone will work out how much fuel is actually used carting a full tankfull and a jerrycan full around (maybe 60 or 70 kilos total) compared to limping from petrol station to petrol station on a max of 20 liters a time. Am fairly sure over a year it would make financial sense but can anyone really think, say, running out of fuel while stuck in a traffic jam for 4 hours for example an acceptable risk?