The bottles depicted by Bumpy are pretty much required equipment for youth groups doing DofE these days. The valve works against an internal spring - you have to unscrew the red cap, then depress it to pour the fuel out - this is a safety feature in that if you have been lax and ommitted to check that your stove is extinguished and set the bottle alight, it will self seal as you drop it! Hence it cannot leak in your pack unless the valve itself is not secured correctly or it is damaged.
Some groups get very up tight if you turn up with, what they see as, dangerous equipment and refuse to allow you to use it.
I know that not every reader will be accompanying youth groups but these bottles really are safer than many other types of container.
HTH
Ogri the trog