Besides money, Kerry has a few additional items he can throw, each of which affects only a certain type of Bushites. Experiment with the brain, heart, and bottle of rum to most effectively take out the bad guys and increase your score!
Shot accuracy pays off, as each successful hit with your primary weapon increases a score multiplier in the upper-right corner of the screen; Likewise, each missed shot decreases the multiplier. When the multiplier reaches 10x, Kerry acquires secondary weaponry in the form of additional money that flies upward at an angle with each shot of the primary weapon.
The Bushite mercenaries will come at you in wave after wave of relentless terror. Fight them off as far as you can, and score as many points as you can. Go get 'em, soldier!