Summer after sophomore year of high school

Hey! I just finished sophomore year and I don’t have any big plans for the summer. I’m doing some STEM activities (robotics, Coursera’s Machine Learning course, USACO prep, etc.) and other stuff I’m interested in but I don’t have much going for me and I’m not doing any summer programs. What are some more productive things I could do this summer? I’m thinking about making and launching a mobile app?
(Also, I know I shouldn’t be doing anything just for college apps but I’m aiming for schools like Carnegie Mellon SCS and Princeton, and I want to do something of note related to my interest in CS that will help me when I apply.)

Some ideas: launch an app, start a business (or volunteer) teaching kids how to code, find a local professor and do a CS research project. Most importantly, start prepping for the SAT/ACT.

Anything productive you do is fine. Even getting a part-time job or volunteering in your community (could be computer related) would be well received.

Use this time to prep for the SAT or ACT. Consider volunteering somewhere and/or get a part time job.

My rising junior is doing SAT prep, just got his first job and Whataburger and is taking a summer class.