We'll admit it—we hardly had to do any work to pick out this symbol. In fact, we just sat back in our chairs with our feet on our desks and let the characters explain it to us:
"They don't kill you unless you light them," he said as Mom arrived at the curb. "And I've never lit one. It's a metaphor, see: You put the killing thing right between your teeth, but you don't give it the power to do its killing." (1.122)
Augustus likes having a pack of cigarettes in his pocket, and he likes putting one in his mouth occasionally, but he never ever lights it. For him, the cigarettes are one area in his life where he can have power over his body and what does and does not kill it. He will bring the cigarettes all the way up to his lips, but he'll never let them have the last word.
In other words, he's giving the ultimate "screw you" to cancer.