Tip #1) If you don't have a daily exercise routine, START ONE! Believe it or not, exercising gives you energy. The more you exercise the more motivated you will be do spend your time doing something of value. Trust me, even though I have an hour and a half less free to do other things on days when I do a long exercise routine, I accomplish infinitely more, and I feel pumped doing it. Plus there are the other obvious benefits of exercise, which I need not mention.
Tip #2) Start working on projects you want to work on, but just haven't. We all have them, ideas that've been floating around in our heads for forever, but just never found their way into reality. Starting them can be intimidating, but ironically enough it's often the hardest part. Get yourself working on something, whether it's the writing you've meant to do, the drawing skills you meant to practice, or the music you've wanted to make, you'll feel like you've done something of value if you spend the time to work on it.
Tip #3) Horrible as it might sound, a summer job isn't necessarily a bad idea. Not only will it look good on a resume, and give you work experience, it'll also help give you some perspective on what life is like for most people after they're too old to be in school. It doesn't have to be full time (in fact, I would suggest against it), but even a part time at Walmart will motivate you to make something of yourself so you don't have to spend the rest of your life there.