I was told that the only time to trust a fuel gauge is when it reads empty!
No reason to go fly with empty fuel tanks? And if stopping somewhere in most lighties, look inside to verify there is fuel. Leaks have been known to happen! Use a dipstick. C182 and others with landing weight restrictions really need a dipstick to back up the gauges. High wings are tough to visually check, so dipstick is again quite important.
As you know what the fuel burn is, and how long you have been turning and burning (add a 15% fudge factor) you can mentally verify what the tanks (and gauges) should be telling you.
Oh yeah, W&B is MUCHO important - especially with 4 up in a warrior. Hope your passengers are all svelte!