See C.J.'sHeroic Sacrifice. Not only does he take out a whole mess of zombies by blowing up the bus, but the flaming wreckage effectively barricades the marina, allowing the others to cast off unimpeded.
Why do they waste so much time rescuing Nicole? Because she's in a gun shop and they're about to leave the mall. They can afford to waste ammo rescuing her because they can stock up once she's safe.
When Kenneth meets Ana, he has a rifle on her and tells her to "Speak." Has he killed anyone "normal" who was simply too shell-shocked from the Zombie Apocalypse to speak?