Carrying spare fuel in trunk--NO WAY JOSE
In over 500,000 miles of local Coupe driving, cross country and touring over long distances daily while exploring this great country over many years--have never run out of gas. And while some don't trust their instruments to be reliable I have trusted same and have never been disappointed with my Coupes. If the instruments fail or work in an erratic manner simply replace or repair same--then trust can be restored!
Perhaps my bladder is trained to run out of holding capacity before the tank runs out of fuel.
As to carrying a container of gas in the trunk-I absolutely see no reason to be motivated into carrying a spare item of hazardous material there.