The odometer is they way to go.
Absolutely. I usually fill up every 250 miles. If I've been driving with a degree of exuberance this means 34 litres goes in, considerably less when touring. 250 miles is plenty long enough to drive without stretching one's legs and having a pee/coffee, and it means I've got at least 10 litres in reserve.
Is the 10 litres in reserve pee or coffee? 🤣🤣
I can manage 2 litres if I use one of my overnight bags these days, it’s solved a problem I have had for some time as I just plumb myself in to a bag under the passenger seat. It’s about the only good thing to come out of this disease (good is a relative term 🤣🤣).
BR
Colin