Wow, If I had three months to just do something, my problem is what not to do.
Let's see. 1. Have fun. Try some new adventure type of sport. Boating, four-wheeling, something.
2. Learn a new programming language. Tons of new stuff to play with here. I do best with self taught but some like classes better, whatever you works for you.
3. Make a new website or mobile app.
4. Volunteer to help out at a non-profit. Pets, orphans, something.