Give all your classmates or co-workers copies of the template - declare war over lunchtime...
Step 1: Materials and tools
This is a cut-out-and-make Instructable.
You need a copy of the template (I work to A4), a cocktail stick, scissors and a glue-stick to make each catapult (though sticky tape may be useful for battle-field repairs). A cutting mat is a lot of help if your work bench is a s rough as mine (my mat is marked in 1cm squares, which gives you an idea of the sheer size of this great weapon).
New for 2009, at no extra cost! A redrawn PDF file of the template is now attached to this step!
The ammunition can be anything that will fit in the catapult's bucket - paper balls, the rubbers off pencils. I shot Tic Tacs at my class - if they caught them before they hit the floor, they ate them.
A pad of paper towel or modelling clay will stop you skewering yourself when you poke the necessary holes in the paper.
Full personal safety precautions can be seen in the video in step five.