How often in the real world does you major apply to your actual job? and How does a major limit the type of jobs you can have?

Kudos for thinking about all of this stuff in advance - You have some really cool experiences ahead of you and the good news is that your choice now is actually much easier than you think it is.

When you go through school you learn a lot of very specific stuff that you may or may not use every day for the rest of your life. That kind of specific stuff is far more broad than you'll apply in any one job. Most likely, you'll learn stuff in college that will help you understand and learn the things that you will need in your eventual career. If you're in High School, it's far to early to worry if specific courses are going to be directly relevant to your eventual job.

If you're lucky, life unfolds as 50% intent and 50% chance. The chance part tends to be a combination of people you meet and interests and skills you'll develop along the way.

To give you an example of a mechanical engineer track winding its way, I'll share my own path:
Undergrad (4 years) in mechanical engineering
A year internship as a project manager (used the engineering stuff a little)
2 years building robots and writing software in Mechanical Engineering grad school (yep, ME's do code, especially in grad school)
6 years designing robotic vehicles and leading teams
2 Years engineering cloud computing
2 more years managing a team of engineers
How do all of these fit together? They're not defined by my undergrad degree choices, but my interest in doing cutting-edge stuff, curiosity, relationships I built over time, and a desire to lead teams.

So, my recommendation is to pick something that sounds really interesting to you and don't sweat it if you end up changing courses later. You never know what opportunities will pop up and give you a new road to follow.

I will say one thing - an ME degree does give you a broad set of skills and background - something that something narrow like aerodynamic-paint-pigementation-engineering would not. It will give you a solid technical background and still keep your options open.

The answer to most of these types of questions is that it depends. I went from a degree in Mechanical Engineering to working in product development. I have applied the principles of what I learned in college to my job a lot. It was very rare for me to work the equations, but a deep understanding of the fundamentals has been important to my success.

I know engineers that went into technical sales. They use there education to relate to the customers. Some engineers go into technical sales support, where they build demos and help the customer solve issues. They also use it a lot.

The degree you chose will set you up better for some positions than others. If you get a degree in mechanical engineering, you will not easily get jobs in accounting or electrical engineering. But you can rise up in a company to run a department or head a company that has both under you.

You need to find a degree path to help you do the job that you are passionate about.