As mentioned previously, there are a few things you should try to put into your application to get med schools to take you seriously, all of which require an obscene amount of work through the first three years of college. If you're close to the end of college and you don't have anything to show for yourself (or if you're close to the beginning of college and don't plan on having anything to show for yourself), you will need to take time off after you graduate and do something drastic to improve your chances of getting accepted. There are a few prescribed things you should stick to when taking time off, because even though there are a lot of ways to spend time off between college and medical school, there are very few that selection committees consider to be "acceptable."
Medical schools will definitely respect time used to do research in a lab, especially if you get published. This is basically the same as doing research during the school year, except that it's more like a nine-to-five job and a lot more is expected of you. Because of both of these reasons, it makes it a lot more difficult to dick around while doing research for a full year. You'll also want to find some kind of grant to fund your time off, like a Fulbright scholarship: don't count on your parents wasting any more money on you just because you couldn't keep up with the rest of your classmates. Finally, make sure to make sure to get a good supply of crystal meth or some other strong stimulants, since research is boring as all hell and it's going to take something stronger than your typical cup of coffee to keep you awake.
Doing volunteer work is another option. There are lots of opportunities in this area, many of which are well advertised. For example, Teach for America enjoys sending out spam emails to college campuses in the hopes of reaching that one person on the planet who hasn't heard of them yet. They'll even go ahead and set up an appointment for you to meet with their recruiters without your consent, so you literally just have to show up in order to get a spot with them. There are also volunteer opportunities that allow people to practice bare-bones medicine in very rural parts of the world, especially in Latin America. It is pretty unethical for people without any medical training whatsoever to perform medical procedures on people from other parts of the world who are too destitute to care, but it still makes selection committees go absolutely cuckoo for Cocoa Puffs when they see an applicant who has these experiences.
Other year-long activities that medical schools consider "worthwhile" include getting other graduate degrees, starting your own business, or being someone famous (e.g., the child of a senator). Note that there are certain things that are absent from this list, like improving yourself as a person, or starting a family. Medical schools consider things like these to be a gigantic waste of everybody's time, especially theirs.
Of course, if no medical school accepts you even after you've taken some time off, you may have to consider alternatives such as a Caribbean medical school or even a D.O. program. Both of these types of schools are known for having lower standards than allopathic medical schools in the United States, so they are a viable possibilities for those of you who are desperate to get into a medical school and won't take no for an answer.