I play piano and flute and want to participate in more outside of school. Suggestions?
Ask in http://talk.qa.collegeconfidential.com/music-major/
Ask your band teacher.
Start taking private lessons.
Is there all county or all state band you can try out for?
Is there a local youth orchestra you can try out for?
There are summer camps
Your local youth symphony or other ensemble would be a good place to start, at least for flute.
If you have a local music therapist see if you can do volunteer hours helping with that? If your in/near a city see if there is any type of symphony/philharmonic orchestra or anything. We have a student here who did that and he is now taking a a gap year touring Europe with the music group.
Are you a member of your regional flute club or association? Check out this information on National Flute Association website, they have great resources:
http://www.nfaonline.org/Resources/
Start taking private lessons, auditioning and attending district and state band/orchestra events. Join local youth or amateur ensembles or orchestras. Consider adding a piccolo, as there is a higher demand for more versatile players. Start your own chamber music group! There are a lot of events you can participate in, even if there is no youth orchestra to join nearby. Good luck!