Additional recommendations for things outside of school
https://explorabl.es/ is a great website for introducing concepts rarely covered in school. If you're not sure where to start, I'd recommend the Prisoner's Dilemma one, but really, follow your curiosity!
Wondering what to do for the summer? Here are some programs to check out.
Other great lists exist, so I won't bother reduplicating all their contents:
I know you're all busy during the school year, but MIT's Educational Studies Program runs Splash for high schoolers, in which MIT undegrads teach anything they want (and you learn anything you want) for a weekend. (There are also multi-week long versions called HSSP.) Sign up in late October!
Puzzles are a fun pasttime.
I personally think everyone could read more books (myself included). Below are some personal recommendations, both science-related and not. I would also love to hear your recommendations!
Some science- and math- focused Youtube channels are:
*Note: though I cannot endorse all the content found on these channels, they tend to produce high-quality educational content supported by science.