Junior Year Summer Ideas

Hi there. I’m a high school junior starting to think about what to do this summer to improve my ECs for colleges. Any ideas that don’t involve expensive programs? Also I’m from Seattle so if there’s anything here I could do that would be great. I was thinking maybe a service trip or volunteering at a summer math camp for girls. I enjoy math and science as well as helping others but I’d love to do something a little more in depth I just can’t come up with much. I know that there are some internships available but I haven’t found any that allow for a flexible schedule as I may go on a short vacation this summer. Any suggestions or ideas of what to do this summer would be great!