With a range of about 500 miles on a full tank in a Ducato based van why on earth would you bother with cans of spare fuel?
I wish! About 250 miles on my Ducato before it's time to fill up. Mind you, it is a big coachbuilt so has all the aerodynamic qualities of a block of flats, and I think they fitted a small fuel tank due to concerns over front axle loading.
Still don't carry any spare fuel though!