Make a bow and arrow
Lots of options:
String / elastic
Funky foam (for arrow head)
Craft feathers (for flights)
Either simply find yourself a suitably springy branch to use as a bow and tie some string / elastic on it (use a clove hitch).
A more efficient method is to make a "bundle bow" - you need three straight-ish sticks, one the size of your bow, one three quarters, and one half. Lash/tape the 3/4 sized one to the middle of the largest one, and lash the half-sized one to the middle of this. This'll leave you with a thick section at the middle, slightly thinner just outside that, and the outermost bit even thinner. This gives the right flexibility at the right place. You can add more sticks to this to vary the flexibility. Bamboo canes (apparently) work for this as well.
Make arrows out of bamboo canes - you can try adding weight to the front (funky foam arrow heads), and feathers to the back.
If several arrows are made use string to tie together with a reef knot.