Ever year, I get a series of emails in March when 4th year medical students do not match into residency. In some circumstances, the graduating student may have a "red flag" in his or her academic history. In other cases, it's a matter of bad luck or not applying to enough residency spots.
In general, I tend to give the same advice:
1. Find a research opportunity during your transition year. This will be highly instrumental in boosting your chances of getting into a residency next year. Do your best to get something published.
2. If you have the funds and the time, you can get a one-year MPH. Do you have the time and money to make that investment and to be in school for yet another year?
3. Enjoy that year. Travel. Spend time with family. Play. You won't get this type of break again anytime soon unless you quit working.
4. Finally, there is the practical issue of finances: what do you do if you really need to generate income that year? You'd be surprised to hear what some people have done to make ends meet during that year. You can work at a restaurant, but you will always be tired because of long work shifts. Sounds like residency, doesn't it? You could do some tutoring or teaching with test prep companies. You could work for a library, a public health organization, or a You could also find a "regular" job, but most companies will know that you are probably only interested for a year of employment, so who's really going to hire you? Some consulting firms may. Or, you may get some traction finding a corporate internship within a pharmaceutical or technology company, but these jobs don't usually pay very much. Finally, there are a growing number of startup companies that may have the financial resources to employ a medical school graduate for a year. Look in SF, NY, or Boston for these tech startups.
No matter what happens, do not give up and do not lose heart. You have made it through 4 years of medical school. If you plan properly, you should be able to get into a residency so that you can pursue a clinical career. As a last resort, you can also choose to pursue a non-traditional, non-clinical career and find enjoyment and fulfillment in such a career path. There are plenty of job opportunities for MDs and DOs who did not do a residency.