In my opinion, students really have to have done stuff for all four years in school for it to pay off as a senior. It's almost too late once you are already a senior. But even if you didn't start volunteering and getting active in school till you were a sophomore or junior, you should try anyway. Keep a journal of everything you do. If you are not able to aggressively compete for awards and titles in school, at least compete or exhibit things in your local county fair.
Blue ribbons means first place.
Enter as many contests as you can. Even if you do not win, you are automatically a runner-up or a participant just for trying. It shows you are not afraid of competition. Apply for everything. Leave nothing out.