Here's a ruler by London designer Sebastian Bergne that's specially adapted for shooting rubber bands.
Slits in one edge mean users simply need to wrap a rubber band round one end to create a trigger mechanism before firing away.
Here are some more details from Sebastian Bergne:
Bandit was inspired by the 100s of red rubber bands littering the streets of London.
What at first glance appears to be an ordinary ruler is transformed into a fun product to appeal to the naughty school boy in everyone.
Typology: Shooting Ruler
Manufactured by: L’Atelier d’Exercises
Materials: Acrylic
L 32 x W 3.5 x D 0.3cm