Anything Ты want... journal entries, taking notes in class, doodling, Письмо stories, songs, или poems, Письмо things down that Ты don't want to forget, keep track of your Избранное quotes, use it to make lists, make paper airplanes... the Список goes on. :)
Maybe a diary, или maybe notes for school или for hobbies like if Ты write. или maybe Ты can use it to draw, that's what my cousin does. Just doodle with it. Use it to do your homework on. Anything Ты want!