So, yes, I know that the colleges look at the numbers, the GPA and the SAT/ACT, and extracurriculars and leadership, but what is super important in the application? What should I strengthen in the last year I can of high school what can I do to help boost my chances at any college I plan to apply to?
Be nationally recruited in a sport. 
The most important factor with broadest appeal across all school is to be an under represented minority. Thats something you either are or are not. Being a recruited athlete is not easy or simple even for the top athletes. Being exceptional at something is the key–and that would include being a top athlete.
The link above confirms what I was going to answer (I hadn’t seen it before - great data) - top grades in a rigorous course selection, and then standardized tests. Sure, everyone throws in “holistic”, but being able to show that you can excel over a multi-year period with challenging courses is a much better indicator that you will succeed in college than a great recommendation or essay.
I’d venture to guess that if colleges had to force rank, grades/rigor would significantly exceed standardized test scores.
If you’re looking for that secret other controllable thing that you don’t know about that’s more important than “the GPA and the SAT/ACT, and extracurriculars and leadership” - there isn’t one.
@goddess00:Does the under represented minority have to do anything to strengthen their application and chances for admission?
@Waiting2exhale Absolutely. Everything adds into the chances for admissions. Indeed, if having a high GPA increases the chance of acceptance, and URM status increases the chances for acceptance, a URM with a high GPA has a higher chance than a URM with a low GPA, or a non-URM with a high GPA.
Is OP going for holistic or a numbers only admit decision? Highly competitive colleges or less so?
You don’t get in just by being URM.
What OP can do to “help boost my chances at any college I plan to apply to” is try to learn what each of the targets wants to see, what they say. In holistic, I sucess isn’t just about any predictor of college grades.
Google the College’s “Common Data Set” and look in section C7 to see what they think is important.
Other than the obvious, elite colleges look for students who can benefit colleges in some way. If you can add money, fame, power, connection, political correctness and such then you are a much better candidate than any valedictorian with perfect SAT, love of learning, artistic abilities and dedicated extracurriculars.
Lower ranked and higher acceptance schools need high GPA, high SAT, merit scholars to improve their averages statistics so they even give money for that. High ranking and low acceptance colleges don’t need to buy statistics.
Think outside the box. There are 10’s of thousands who did model UN, or are president of the investment club or whatever. Someone with those things does not stand out. You do not have to do bizarre things to stand out; instead explain who you are, for example by writing about why you do your ECs. (The following is a generality, not directed at OP) Do you do Model UN because you can’t think of anything better? How boring! Or do you do it because your Mom emigrated from the middle east and you feel that part of the world gets a bum rap, so you want to see how international organizations can combat the bum rap, and, by the way, you are obsessed with middle eastern cuisine so cook one new middle eastern dish a week, that you share with the refugee family down the block.
Can you see how this kid, whose EC is Model UN stands out? It’s not because of any achievement on paper, but it tells the AO about them. And of the tens of thousands of model UN participants, there’s a very good chance that none of them would, or even could, write that essay.
The CDS is one data point only. It is not policed or verified in any way. It can mislead, if you think it’s an absolute check ranking of what matters- and doesn’t even begin to reflect the personal traits top colleges look for. User beware.
And big tip: it is NOT about a kid’s potential fame. It starts with what you offer to the aggregate four year experience. Nor about college grades.
Such an interesting example, @cinnamon1212 . Even your brief desciption adds interest.
But the colleges are looking for your self awareness and insights relevant to the four years. So the fact you love to bake cupcakes or walk your dog may not be an it. It may be “you,” but not what shows them your fit and contribution to that college.
@lookingforward I just made that up 
But you are right, it’s not enough to say you like to bake baklava, you would need to reflect on your experiences/direction/life. Why baklava? What does it mean to you? How does it tie into your future etc.
Also someone in sales told me – always show the other side what’s in it for them. So show the colleges what’s in it for them – what you would bring to the campus – what do you add? And ideally, what do you add that no one else will?