Civil Disobedience by Henry David Thoreau LD novices, start here. If you’re going to debate CD, you might as well read the core source document. HDT can sound a little over-the-top at times, but his influence on Gandhi and King is not to be ignored. Also, it’s short, and available free online (e.g., as a Kindle book).
Justice: What’s the Right Thing to Do by Michael Sandel This is a very readable overview of things like rights and morality. Sandel covers the classical thinking, but he’s not dense or confusing, and almost everything in here is relevant philosophy for most LD resolutions, and useful philosophy to keep in the back of the mind for PF.
Second Treatise of Government by John Locke On Liberty by John Stuart Mill These are the classic original texts, the former on rights and the social contract, the latter on freedom and its limits. Both relatively short and free online. They are not only useful for debate, but for many other subjects that will arise in one’s high school career, one’s college career, and perhaps even one’s life in general. Knowing what is in these books, and being able to quote them appropriately, will serve you well.
Nigel Warburton Warburton is another great explainer. He’s not essential, but you may like him. For instance, his A Little History of Philosophy, which is just that, is a great start for learning things beyond the ethicists we usually cover, going back to the beginning and the hifalutin Greeks. Among other works, he’s also got a chapbook Free Speech: A Very Short Introduction, and a very absorbing podcast, Philosophy Bites. He’s a good go-to person if for starter materials.
A Theory of Justice by John Rawls Modern philosopher Rawls developed ideas of distributive rights, including the famous veil of ignorance. If you read this book right up to the first mathematical proof, around page 75, you’ll have read all you need. If you can read past page 75 and still understand it, you’re a better man than me.
Anarchy, State and Utopia by Robert Nozick The yin to Rawls’s yang (or is it the yang to his yin?). Rawls is liberal, Nozick is conservative. Take it from there.