This symbol's pretty easy to pick up. The rules at the Creek state there's no smoking allowed (plus it's state law), and smoking anyway is a relatively tame and easy way for Miles and his friends to buck authority:
The Colonel gave an obligatory laugh, then asked, "Want a smoke?" I had never smoked a cigarette, but when in Rome…
"Is it safe here?"
"Not really," he said, then lit a cigarette and handed it to me. (128before.90-92)
Of course, the characters know that smoking cigarettes is self-destructive:
[Alaska] smiled with all the delight of a kid on Christmas morning and said, "Y'all smoke to enjoy it. I smoke to die." (110before.44)
But clearly, cigarettes are used for more than self-destruction and social acceptance in the novel. Miles and the Colonel smoke to have fun, but they—especially Miles—also smoke to cope with Alaska's death.
The Colonel sat down next to me in religion class, sighed, and said, "You reek of smoke, Pudge." (8after.5)
The safest place to smoke is the Smoking Hole, and slowly that place becomes a symbol for something more than just smoking and rebellion. Its nature is secretive, making it not only a safe place to smoke, but also to spend time with friends.
Not safe? I thought. It's the safest place to smoke a cigarette in the known universe. (67before.12)
The Smoking Hole is the place where Miles leans on Alaska after he realizes his parents are leaving for Thanksgiving. The Smoking Hole is where Alaska finds the white daisy she puts in her hair. Miles ends up thinking at the Smoking Hole after he and the Colonel have their big fight. And the last time we see the characters at the Smoking Hole, they each throw a cigarette in the water, a ritual for Alaska.
I was not religious, but I liked rituals. I liked the idea of connecting an action with remembering. In China, the Old Man had told us, there are days reserved for grave cleaning, where you make gifts to the dead. And I imagined that Alaska would want a smoke, and so it seemed to me that the Colonel had begun an excellent ritual. (46after.23)
So cigarettes and the Smoking Hole are more than just ways to rebel against the authority of the Eagle. They connect the characters.