I don't routinely carry spare fuel in a vehicle but I do store fuel for a tractor and other equipment. (Diesel, Gasoline, Kerosene) I got tired of the cheap plastic cans and other junk on the market. I found these new Jerry cans sold by Deutsche Optik. http://deutscheoptik.com/Militaria-Tools/NATO-20-Liter-Jerry-Can-SET-OF-FOUR.html
If you buy four the shipping is free. You can also purchase any number less than 4 and pay for the shipping.
I don't know if they are the sole source for these cans but I believe they may be.
They aren't cheap but they are very well made. These have proven to be the best fuel cans I've used. The 20 liter (5 gal +/-) are marked "Not for fuel use" in order to comply with the bed-wetting liberals on the left coast, but they make Great fuel cans!
Not attempting to sell anything just thought I'd share for the folks out there that may be in the market for high quality Jerry Cans. For something that you only need to buy once, these get my vote.