I don't really think you have to travel the globe working on small projects with Thinking Beyond Borders, volunteer in a medical clinic in Zimbabwe, or move to Israel to learn Hebrew as some of my friends have done to make a gap year a productive and fulfilling experience. They actually felt like they paid a fortune for an organized gap year program and could have done something worthwhile on their own. I do think you need to spend the time working, volunteering, learning, and working, and to make every effort to ensure that the year is a fulfilling, productive time of growth in your life.
The first task on the to-do list would be getting a job. You need to have daily structure, accountability, and the feeling of accomplishment at the end of the day. Even if you are only scooping ice cream or selling tee tee shirts, you will be earning money you've made and doing something with your time. However, I would try to find a job that isn't a typical teenage one to have more of a challenge and to work amongst adults. Most employees at places like Baskin Robbins are high school or college students there part-time, and it might make you feel a bit out of place being in-between. Also, the hours in retail tend to shift more. I would sign up for a temp agency and try to land a long-term temp job. Many of the temp jobs only require a high school diploma and proficiency at typing and computer skills, which I'm sure you have. You could also look for internships in areas that interest you.
Volunteer. It's good for your community and your soul. You could walk dogs at an animal shelter, help kids with their homework at the Boys and Girls Club, keep an elderly woman company for a spell in a nursing home, or do something else that interests you and that would be helpful. Hospitals often have organized volunteer programs, and if that's of interest to you it would be great. I am involved in the music program at the hospital at my college, and it's fabulous. I just bring my guitar or my ukulele and sing for a patient. It helped to lead into the internship I have with the hospital this quarter. If you're not a musician, there are still other creative ways you can help.
Learn. If there is a community college near you I think it might benefit you to take at least one class in person there just to stay in the routine of having an academic challenge, and to give you a bite-size taste of college. Many community colleges let you enroll for just one course, and you might be able to take it on a pass / fail basis so you wouldn't have to feel as concerned about your grade. In addition to taking a class in person, explore online options. I know you're interested in writing, and there are several colleges that have online classes open to the public for various mediums. Stanford has a fantastic, very well-regarded online certificate program in writing in addition to several other courses.
https://continuingstudies.stanford.edu UCLA Extension also has numerous courses. There are several universities that now offer FREE classes, so if money was a factor you could take advantage of them.
Here's a list: http://thesoultodare.blogspot.com/2012/12/learning-from-best-for-free-in-your.html
Travel. You really don't need to trot over the globe. Save up your money from working and plan on traveling somewhere, even if just for a week or weekend. Sometimes you can find surprisingly inexpensive flights to Costa Rica, and the costs there tend to be low. You could just go somewhere in the US that you've never been. The point is to leave your comfort zone for a few days, shake up your routines, and explore someplace new.
Good luck to you!
~ skylark : )