I was the manager of our school's bookstore too so that took up a lot of extra time.
The biggest piece of advice I can give to kids going to HS is to not take yourself too seriously. I did and I wish I hadn't. Also, don't be worried too much about what other people think of you. Most of the time everyone else is just trying to fit in too and probably aren't even paying attention to you. LOL All of this is advice I wish I had given myself back in the day.
I promise that once you are out of HS you will realize how petty and immature HS is compared to the big world.