So, yeah, about that mountain-climbing hook... Or was it a hook used for trawling dead bodies? Or was it... Wait, we never really do find out what that hook is actually supposed to be used for.
What we do know is that it's a symbol for the angry, defensive, delinquent exterior Bone puts on in response to Glen's abuse. How did we come to that conclusion, you ask? First of all, for all thrown-out trash that Bone happens to find in a river, the hooks really capture her imagination. The aspects of the hooks that fascinate Bone are pretty odd:
I wanted one of those hooks, wanted it for my own, that cold sharp metal where I could put out my hand and touch it at any time. (12.78)
It's not that Bone just likes shiny objects (who doesn't?); it's that she finds a kind of safety in the scary dangerousness of the hook. That makes sense when you think about the way she wraps the chain around her as if it offered some sort of protection, right? "But wait," you might ask. "How does masturbating with a chain offer any sort of protection?"
Well, folks, that's where the "symbol" part comes in. Let us direct your attention to Exhibit A:
Up there it was safe and out of sight, a talisman against the dark and anything that waited in the dark. It made me stand taller just to know it was there, made me feel as if I had suddenly become magically older, stronger, almost dangerous. (13.1)
See, this passage tells us two things: the first is that Bone feels the need for some kind of almost symbolic protection against some kind of danger or evil (see analysis of "Booker's Seven Basic Plots" for an account of how Glen is a "dark power"); the second is that the hook will protect Bone by making her feel "older, stronger, [and] almost dangerous"—which tells us that right now she feels young, weak, and whatever the opposite of dangerous is. The hook is thrown-out trash—like Bone—but it's thrown-out trash with an attitude, which is what Bone would like to be.
The hook protects Bone by allowing her to become a more courageous—and more dangerous—person. The added courage the hook gives her allows her to do some things she wouldn't otherwise do, like break into Woolworth's.
Why does Bone break into Woolworth's, by the way? Well, no matter how much courage she gets, there's not very much Bone can do about Glen, or about James and Madeline Waddell and all the other people who call her trash. She's still a child, after all. She can't escape these people no matter how hard she tries.
So what does she do? She goes after another one of her enemies, instead, one who is easier to target. In this case, it's Tyler Highgarden, the dude who banished her from Woolworth's after she stole some Tootsie Rolls. In the grand scheme of things, of course, Tyler Highgarden is small fry, but he gives Bone the chance to act out some much-needed revenge. It's no surprise that the Woolworth's chapter ends with Bone thinking about pulling up the Waddells' rose bushes. Her revenge hasn't just been against Woolworth's; it's really been against everyone who puts her down.