Senior year in high school is one of the most exciting times in most people's lives. Not only are classes (hopefully) a little easier, but the realization that graduation is almost upon you can give hope to even the weariest student. My advice would be to live it up; enjoy your last year with all of the friends you've grown up with, spend time with your family, go to all the sporting events and cheer on your soon-to-be alma-mater.
I'd like to also encourage you to do these mundane tasks as well:
1)FILL OUT SCHOLARSHIPS. The sooner the better! Start doing it the first week of school if you can. There are many scholarships out there, and some are perfect for you! Every little bit of financial aid helps.
2) Study for, and take the ACT a fourth, fifth, maybe even sixth time. I know it's long and painful, but you will definitely not regret it!
3) Find out where you want to live. This is especially essential for those that plan to move more than three hours away from home, and who don't plan to live on campus. The housing market fluctuates daily, so it's helpful to be knowledgeable in the local area around campus before it's time to pick one out and move in.
4) Find a cheap place to buy your books. RENTING IS A REAL THING.
5) Don't succumb to senioritis. Studying never ends. Once you leave high school, go ahead and start brushing up on all of those basic classes you took freshmen and sophomore year in high school. You'll be thankful you did when you get to the midterm your first semester in college and you realize that the professor accidentally skipped the part of the book that the majority of the test is on.
All this being said, don't stress about it too much. I'm a firm believer in whatever happens, happens. That doesn't mean you should be lethargic. It just means you should live prudently, give it your all, and face every oncoming obstacle with optimism. In you the words of Rob Schneider, "You can do it."