Use basic pioneering to construct a ballista and fire bean bags (or balls, screwed up paper etc.)
Bamboo canes, elastic bands, small plastic bowls (drilled with 3 small holes @120 degrees), bean bags,
Using the canes and elastic bands (or string if doing lashings) make a triangular pyramid. On one face attach the elastic bands to each corner of the pyramid - attach the other ends to the bowl. Place bean bag in bowl, pull back and fire. We have competitions on accuracy of firing by having buckets as targets. See attached photo.