A big +1 to the recommendations for math. The more math the better. While there's a very good chance you won't actually use math at all on the job, it is the best (or only?) exposure you're going to get to logic in high school.
My next biggest recommendation would actually be a good class in writing, if your school has one. Specifically something that focuses on constructing arguments in writing. Any job in software is going to require you to communicate with others, often times through writing. Getting a leg up here will help a lot. As an added bonus, it will help you through any future classes that make you write papers in the future (you'll do so many that you will be able to knock them out quickly).