What to do over the summer to build resume as an incoming college freshman?

I agree with onlooker. Especially in regards to a foreign language or reading/watching different things about the world. Most colleges and businesses would be impressed if they just see that you're well informed about what's going on in the current world. They'll also be impressed if you can communicate with others, not just in languages, but of different social classes and mental states as well.

I suggest checking out websites like Craigslist. They often have plenty of opportunities for local volunteers (some even pay). If you see something you might like but there isn't anything good available, you can check out recent YouTube videos or join Facebook groups of those jobs, and do them locally or remotely (online). 

Some suggestions of jobs are things like tutoring students. I once knew a guy who was tutoring Japanese kids, helping them learn English. I don't think he was fluent in the language, but he could hold a decent conversation, especially with a child. You could also teach math or even English to struggling English students.

Another suggestion is volunteering at summer schools or summer camps. The organizer I'm sure would guide you through on what to teach or how to interact with the children.

I know there's also plenty of places holding food drives and handing out meals to the homeless. Some volunteer to even working in homeless shelters, sometimes having to help children get dressed and ready for school! (I really like children! Can't you tell?)

Do a full-time volunteer gig at a non-profit for the entire summer and learn everything you can about the operation.  Then summarize the experience in writing as if this was a formal term paper.  Save this paper until you interview for an internship, and then share it.  No one else will have a paper like this.

You can't get a job, research position, or internship as a soon-to-be-freshman that will be related to your career. Internships that enhance your post-college resume don't happen until at least the summer between your sophomore and junior years -- when you actually have some useful knowledge and talent to offer the company providing the internship. 

You can do any or all of the following:

* Get another high school summer job. Learning to be a good employee even if you find the work boring is a good skill to have.

* If opportunities exist this summer, look at volunteering for an organization that you support.

* Teach yourself something whether it is how to create a website, manage a check book, plant an organic garden, learn the rudiments of a new language, or memorize the map of the city where you'll be going to school I the fall.  Take an online class.  Learning to be a self-motivated learner will be essential. You're going to a T20 university where everything is going to be competitive and there won't be a lot of hand-holding.  

Your goal this summer is to enhance your own personal experiences and breadth of knowledge.  

Read books, watch documentaries, learn how to cook, study a foreign language, learn an instrument, go hiking, take photos, write poetry, grow houseplants, volunteer for a good cause, take singing lessons -- it's all relevant. Not only does it help us meet and connect with all sorts of different people, it allows us to think outside the box. Successful people are generally well rounded and able to talk about a lot of different things.