Mike Mulligan and his Steam Shovel.
I know that doesn't sound like much of an answer on its own, but let me explain.
In my favorite Ramona book, Ramona the Pest, there's a scene where Ramona's kindergarten teacher reads Mike Mulligan and his Steam Shovel aloud to the class. After storytime, Ramona has a burning question for Miss Binney: How did Mike Mulligan go to the bathroom when he was digging the basement of the town hall?" Then, of course, everyone else in Ramona's kindergarten class wanted to know the same thing. Miss Binney's response, one all of us can afford to remember:
"The reason the book does not tell us how Mike Mulligan went to the bathroom is that it is not an important part of the story. The story is about digging the basement of the town hall, and that is what the book tells us."
The reason The Hunger Games does not tell us how Katniss knows where the cameras are, or the deep and detailed history of Panem, or how Haymitch won the Hunger Games other than Peeta's observation that Haymitch must have outwitted all his opponents, is because they are not important parts of the story. The story is about Katniss participating in the Hunger Games, and that is what the book tells us. It's not that I discourage debate and exploration of books, but you know, my fellow readers, we can't always get what we want (and if we did, would we want it anyway?). Most importantly, we can't always get what we want from a first-person novel. This is something I wish more writers as well as readers would realize. Katniss is too busy trying to get through the next five minutes to take the time to explain to the reader how Panem came to be. Is it important to the reader? Yes, and believe me, I'm dying to know all the background, too. But this is a first-person novel, and it's Katniss's story. If I haven't been paying attention to the last 75 years of the Hunger Games, that is my problem and not hers. Sometimes, the things we want to know as readers simply don't matter to the story the character is telling. I think this is something that too often gets neglected in first-person books. The Hunger Games is a great first-person novel because Katniss doesn't break the fourth wall, just like Inexcusable is a great first-person novel because it knowingly and deliberately breaks the fourth wall. Many of the first-person books I read last year would have been much better done in third because the author could not put his Mike Mulligans aside. Instead, I got books where I thought the main character knew I was there but I couldn't be too sure, and just to be sure I understood him (or her), he would take lots of aside time to explain the workings of his world to me. Nothing kills a promising first-person book like a data dump. Or a dirt dump, since we're talking steam shovels here.
Mike Mulligan, by the way, is also my answer to the question of "Why didn't J.K. Rowling reveal that Dumbledore is gay during the course of the HP series?" It works. Try it!