For books, look up the topic you are interested in and then find books about said topic. I think it'd be best for you to find something you're interested in since you'll have to demonstrate it in your PS. Tbh, I only read one book and then talked about other TED talks and articles.
For essay competitions, enter the Young Economist of the Year and maybe one more. There's another competition called the John Locke competition which I didn't enter but I know some people who did.