My project is "write a 200 word letter that could be placed in a time capsule to be read 100 years from now. in your letter, advise students your age about three things they need to do to keep themselves, their families and their communities healthy."

can someone suggest some topics to put in the letter? id be most grateful.

Well you could say somethings about how your life went, the mistakes that may have taken place and the Great things that happened. If you fell uncomfortable about any failures thats fine. But by teaching those people the mistakes you are teaching them on how to aviod them. anyway, you could also tell about what went on in the world around the world. That's most of what I can think of right now.
 
I hope this helps.