Regular exercise book,
A working brain.
First, get a regular size exercise book. But, the bigger the better. Some types of paper wouldn't work, so it's better not to use counter books.
Step 2: Cut...
Tear about an inch off the edge of the length of the page.
Step 3: Roll...
Roll it up till about half the length... then flatten it.
Step 4: Folding...
Then fold the flat part in half... as many times as possible. I managed two, which is usually the max.
Step 5: More rolling...
Then roll up the rest of it.
Step 6: Ready the cannons and...
Now fold it in half... It might be really hard so you can use a tabletop to help... Aand your'e done!
Step 7: SHOOT!
Just added this step in case someone stumbled onto this without knowing how to use it. Just use your fingers as a slingshot. This can be really painful, so be careful!