Slight tangent here, but back when I owned a 1995 BMW 525i I discovered while browsing a parts catalog that BMW had developed a special emergency fuel jerry can[0] that slots into the spare wheel. The can was flat bottomed but the sides curved to fit inside the spare wheel (it was a full sized wheel back then) and it had a removable metal hose that clipped on the top when not in use. It was a fantastic piece of design. It held 9 litres if I recall correctly, so it wasn’t too heavy to carry when full (of course, you store it empty, and if you run out of fuel you take the empty can to the nearest fuel stop and fill up there).

I was lucky to find one on eBay that was in new condition, and I kept the can when I traded in my BMW for another BMW, unfortunately my current car uses runflats and hence no spare wheel, so I just keep my jerry can in the garage.

[0] https://classics.pt/images/artigos/deposito-roda-suplente-9l...