As Leslie said, math is very good. Subjects that apply math, like Economics, can also be good, as a way to get you thinking about how math can be used in the real world.
Some high schools over programming classes. These, especially the AP ones, are very valuable.
Whether you can take any programming classes or not, if you can start to practice programming on your own, it will give you a huge leg up. https://www.codecademy.com/ is a good resource for this, and there are others. This also can help you determine whether you are actually interested in following a career in programming.
As you reach your junior and senior years, look for colleges which talk about their computer science programs, and if you can, ask about majoring in Computer Science.