I would consider a tank that has no fuel visible in it to be empty for endurance planning purposes and 10 gallons for WnB.
Here's how I manage my fuel reserves, starting with how I did it in my M20F prior to the engine monitor.
Always look in your tanks. Even if you stop for lunch and come back out, look in your tanks. People steal fuel, sump points sometimes stick, line guys fill you to the tab instead of the rim, they fuel the wrong plane, et cetera. A member here didn't place any fuel order and came back to his plane filled with Jet-A; had he not checked, it could've killed him.
My M20F holds 32 gallons on each side. For long trips, I would start off on one tank, climb out on it and switch after three hours or when the engine stopped (if I run a tank dry, it would usually tank about 34 gallons). That, to me, guaranteed that I had at least 3 hours remaining since you burn more on the climb and I didn't include what I burned on the ground. I wouldn't even notice the imbalance. Some pilots like to switch every so many minutes. I don't like this approach as if things got down to the wire and I were into my reserves, I would not want them split between tanks with uncertainty. I also regard switching tanks as having an increased risk factor. I read an account of a vintage Mooney owner who had the selector handle come off in his hand while turning it. Fortunately he was able to access a pair of vice grips from his toolbag to successfully switch tanks.
After getting my engine monitor and being certain of its accuracy, I started burning 16 gallons off of one tank, switching tanks, and not switching back until either I burned off 32 gallons or was less than around 12 gallons calculated remaining on that side and coming in to land.
I do not trust panel mounted fuel gauges, though the wing-mounted gauges are excellent to ensure you have fuel in your tanks if the needles are bouncing.
I have not yet developed a full methodology for managing fuel in the rocket. Fueling is much more complicated with the long range tanks and flappers on the inboard tanks and I don't yet have it down to any sort of science so I carry more fuel than I need for my trips.