Attempt to bequeath your future self a kinder, more joyful, more competent person. This might involve:

• Learning new skills - eg coding, managing some contractors, research, event organisation
• Getting into the practise of doing things - build a website that you think should exist, run an event you would attend
• Spend a portion of current resources effectively - set aside some resources, do some research, tell others what you did
• Learn what you like - what makes you smile? What do you really strongly endorse
• Get some mentors - write to people you respect asking them for tips on how you could improve
• Get a good sleep and exercise schedule - many people struggle with this later so it's good to get it locked down early. 
• Get on top of your emails, and social media time - many people struggle to wean themselves of email burnout or social media addition. You could get ahead of that
• Look into different project management systems - often these help people get more done
• Take time to empathise with people in different worlds to you - you could watch youtube videos of people in poorer nations talking about their situation. GiveDirectly has a load of these I think 
• Gather resources - your future self may have projects they want to work on. Earning money and putting it aside will give you more options
• Build a close network of like minded ambitious people 
• Learn how you learn - you can probably get much more done at high school than you are. I wasted lots of time not realising this
• Introspect about who you want to be - what are your key goals? how would you know if you were closer to them
• Consider not being involved - often the first community one becomes involved in can be an unhealthy relationship. It's good to spend some time considering the alternative. You could work hard and have lots of nice things. And that would be okay. I don't say this to say EA is bad, but to say that if I were your friend I would want you to do things out of joy, rather than obligation^[1]

You are probably right that it's hard to make concrete improvements to the world right now, but you can give a gift to your future self of a better situation. The key is for that to be something that that person will endorse. Increasing their competence, joy, kindness and optionality seems likely to be good. 

1. ^{^}

   Unless you become a billionaire in which case I want a bit of obligation, sorry

I second Nathan's answer, but besides that here are a few programs specifically for HS students you might be interested in.

• SPARC (deadline closed for this year)
• ESPR
• PAIR
• Non-Trivial

I'd also recommend applying to those university programs! When I was talking with the organizers of those programs at EAG, n=3 seemed to believe it'd be perfectly appropriate for me to apply. I suspect other programs would also (major caveat: may only apply to non-residential programs for <18 for legal reasons).

(also, Yarrow B's answer is a joke, but, anecdotally, a major failure mode of young EAs are becoming too dedicated and sacrificing all their other interests and such for it. )

Their suggestions are relatively abstract, but you might consider reading Katja and Robin on the general topic of whether to focus on contributing money vs other things when you're young.

i highly suggest reading the sequences.

if you suspect you might be capable of it, you could also start reading about alignment and potentially contributing to it. i know of at least one whose been doing (imo good) alignment research since they were in high school. many working on AI catastrophic risk (myself included) believe there's not much time left for you to have a career. you may want to look into those arguments.

Abandon your friends and family, join a rationalist group house in the Bay Area, and write 100,000-word essays about your priors for your AGI timelines and p(doom).

Just kidding!