My first car was a twenty-year-old Mini, and it developed a fault whereby when the fuel gauge got to half, it plunged to zero. After having to call out the AA twice when I'd misestimated the amount of fuel I actually had left, once in a very isolated area, I developed the habit of refilling the tank religiously when it dropped to half-full. This has pre-emptively solved any number of problems, even when I graduated to cars with working fuel gauges.