What is a good way to spend my summer to look good on an application for elite colleges?
Colleges just want to see that you are spending your time in a way that is meaningful to you (i.e. not just watching TV all day everyday). Some things you could do: volunteer, intern, get a job, etc. None of these things are going to guarantee admission to an elite college, so do something that you are genuinely interested in because it will be a big waste of your time if you do a bunch of things that you aren’t interested in and you end up getting rejected from your dream schools.
Get a job and learn what it is like to be in the workforce.
Do what genuinely interests you, and find ways to achieve big things in that particular field. These achievements might need to come later on in junior year, but it’ll be great if you know about relevant competitions, programs, internships, etc, right now so you can have an idea of what you might wanna do. You could also create your own meaningful projects. You might already have incredibly meaningful ECs that you could also be working on.
Assuming you’re not done with standardized testing - I also think you should take a practice SAT AND ACT this summer. Find out which test you do better on. Study to increase your score (tons of resources and book recommendations on this site alone!) and take more practice tests. Try to get the tests out of the way by the end of first semester (1500+, 34+).
Most of all, manage your time and enjoy it. I’ll be a tough year, but you can at least mitigate it by doing what interests you.
Anything constructive is equally fine. Work, volunteer, take classes, do research – whatever interests you. No summer activity (unless perhaps you are an Olympian. cure cancer over the summer etc.) will get you into a college or keep you out of a college.
And as an aside, don’t live your HS years with the sole purpose of trying to get into an elite college.