Several years ago I run one of my previous bikes (2004 BMW R1200C Montauk) dry. Fortunately it was ~ 1000 yards away from a petrol station.
the Wifey and I pushed the bike at the slight incline to fill it up. The incline was insignificant while riding, but rather meaningful while walking the bike...
I run out of gas twice: the first and the last time. Since then, I ALWAYS top off between 1/2 and 1/4 to empty.
So far, so good.
Mind you, our rides are between 75-175 miles and in the known topography, most of the time. It is pure leisure riding: no bad weather, no rush hour, daytime most of the time, avoiding riding after 4 PM Nov-Jan (white tail deer rut season in Texas Hill Country).
My wife's bike ran dry as we were crossing the Navajo reservation near Mesa Verde in 1977. (It was my fault-- long story.) The gas in the 1L bottle for our SIGG stove was enough to get us to the next gas station. It hasn't happened since then. I don't know that I'd carry spare gas for such a low-probability event now; perhaps it would be different if I ever traveled where gas stations are 50 miles apart.
Gasoline is nasty stuff-- corrosive, flammable, with a smell that's very hard to clean up. I'd hesitate to put it in my under-seat trunk or cycle luggage, even in a specialized bottle. Maybe in an external container attached to the underside of the luggage rack. If I'm reading the specs correctly, the 1.5L bottle you cite would fit in this carrier https://twistedthrottle.com/shop/lu...-includes-storage-tube-and-mounting-hardware/