Well for one you're best off focusing on learning what you can "ahead of time" solely for the courses you will be taking next year. I don't think it is a good idea to try and get a 2 year head start on a class like organic chemistry, you're going to need that material fresh in your head during that semester. A high school senior/college freshman's brain can only handle so much information. Part of the process is maturing to the point where you can intellectually handle the learning experience of a class like organic chemistry, which is not meant to be easy.
Most schools go straight from freshman chemistry to organic in your sophomore year. This is basically the chemistry weed out course. Students that can't pass won't get a chemistry degree.
But don't worry about it until you get there, or at least next summer before you take the class. You should have a hard enough time in freshman chemistry/other classes as it is unless you are just the absolute best of the best, in which case you should have taken a senior level high school course that covers a moderate level of freshman chemistry, and taken (and passed!) the post-high school achievement test prior to college that allows you skip freshman chemistry and head straight into organic.
I took chemistry 3 in high school, but damn sure didn't even think about skipping freshman chemistry.
As for additional courses, I would suggest taking some neuroscience classes in your 3rd/4th years if you want to increase your chances of success at medicinal chemistry down the road. Also inorganic chemistry in your 3rd/4th year. Molecular or cell biology, or even virology, are other worthwhile ones. But none of these are easy.
Your school probably has some strengths and weaknesses as far as courses offered go. You will have to see what is offered. There could be some special chemistry courses you may find interesting.
Above all don't be in a rush to blow through the process. If you want to get ahead, perhaps you should try finding the course websites at the school you will be attending next year and see if they have a website where you can just hop on and download things like lecture notes or assignments. The semester is close to over, so usually if the information is accessible, you can get virtually the entire semester's files ahead of time. Or just find the syllabus, buy the textbook and read that.
Else you're probably just best off watching scientific documentaries on youtube or that awesome free online documentary movie website. Or get stoned and play video games, drunk and party... you know, things that normal high school kids do. ;-)
