My advice would be to use your summers and time-off wisely. Find something you're passionate about and start volunteering. If you're interested in the medical field look for ways to help with hospitals or retirement homes. Also, you will need letters of recommendation, so start building relationships with people in your community who are doing the types of jobs you are interested in. Get involved with organizations that go out together and volunteer; this could be churches, rotatory clubs or organizations at school. If there isn't a volunteer organization at your school, you should start one! Becoming part of a volunteer organization helps you meet new people who can show you more opportunities.
Finally, do something that is just for you - something that makes you unique. Paint, dance, go bird watching, blog or create video tutorials. Cultivating your interests will make you a more interesting person!
Colleges, scholarship essays and teachers have asked me many times why I have chosen my major. It was nice to be able to say, "Because once I had a summer job that opened my eyes to the rest of my life."