My personal belief is that you should take the time in high school to explore and find out what you love to do.
This counts for both academic, as well as extra-curricular activities. I would take whatever courses you think you might enjoy. This might include anything from drama or art, to history or math. As for extracurriculars, look into sports, or student activities where you need to work with others in a group, such as dance, yearbook, or student government committees. You might very well find something you really enjoy doing, and it is often these non-academic qualities that will help you get accepted.
However, there are a few courses that will be a great help that I believe you should take, and these are the basic science courses that you will be tested on by the MCAT. These courses are at the grade 11-12 level, and include: Physics, Chemistry, Biology. I would also recommend you fit Math and English in there, unless there is an alternate class you really love. I know this takes up a huge amount of time, but these courses are absolutely fundamental for a science undergraduate degree in university, for the MCAT, and also eventually I believe, for medicine itself. If you take public speaking or debating, and really practice at it, it will be a great help in developing
your poise when you need to interview for medical schools.