Freshman year is the time of experimentation. I, myself, am only one year ahead of you. Although, I do believe that being on this forum for a while now, I’ve gained a decent amount of knowledge when it comes to college admissions.
Now, I’m going to repeat the very thing that several people have said before me: Do what YOU are interested in.
Don’t attempt to take part in activities because they align with some sort of advantage in college admissions. Colleges don’t want the same applicants every time. They want to see your passion in a certain field, not you spread all over the place in every single club.
During freshman year you should probably try out 5-7 different clubs (if possible) and narrow it down in the coming years to your 3-5 most enjoyable ones. Also, make sure these are clubs you are good at. The ones you enjoy are often the ones that you excel in. The best thing you can do is try to gain state and national recognition in the clubs that you do join, because this will show colleges your passion and your effort put into that specific activity. Also, writing about those clubs in your essay(s) wouldn’t hurt. In fact, it would strengthen your application quite a bit.
Since you’re not able to take any AP’s, I would just familiarize myself with what AP’s are and during sophomore year, if time allows it, try to self-study a couple since your high school lacks opportunity when it comes to early AP’s.
Only take subject tests when you finish the course, preferably when that course is either honors or AP. Subject tests require a certain level of proficiency so studying for them without the course is going to be quite difficult. Seeing by your AP situation, you’ll probably be taking them junior year.
Good luck, pal. You’re in for one long ride. And so am I.