forgot to mention... The old military gerry can is so well engineered that it hasn't been improved upon in over 60 years.
Some of it's features.
3 handles: carry one in each hand using the center handle, or 2 in each hand using an exterior handle. Also good for fire bucket chain style passing, as there's more than one handle to grab.
Built in air reservoir: top of can is higher than the spout so you don't overfill it. automatically makes an air pocket.
Stamped sides: increase strength, but they face in so it doesn't interfere with stacking.
single welded seam: single seam means no corners to leak, only 2 pieces of steel used to make the container.
egg shaped spout: designed for optimum pouring, there's a small baffle behind the mouth that allows air in so the gas doesn't gurgle out, prevents the need for another air release valve.
cam action rubber sealed spout: uses simple design to open and close without the need for tools. locks up and out of the way when pouring.
Stackability: stacks in a bevy of different positions.
They were designed by the Germans, but have been adopted after the war (WWII) by every major army. They are probably going to be the military/Recreational fuel container of choice for another 50 years.