Volunteer work is one of those things that you need to have on your medical school application, for a number of reasons. First of all, every other med school applicant will have it on their application. So if you want to be a competitive applicant, it is one of those things you need to have on yours as well. Secondly, not having volunteer work on your application is like directly telling the selection committee that you have always hated poor people and want to deport them all to Mexico. Since this is looked down upon for the most part, it is best to avoid the whole situation in the first place.
You may be under the impression that medical schools like applicants who talk about medically-related volunteer work, but this is not necessarily the case. Medical schools know that most people who have done "medically-related volunteer work" have not done anything more than taking people's heart beats or babysitting sick kids in the hospital's surgical ward.
The easiest way to have volunteer work on your application is to lie about what you've done. The only problem with this method is that if you get asked about what you did in an interview, you will need to be able to talk at length about how much you accomplished and how much it meant to you. If you go decide to take this approach, make sure to rehearse your story so that you know it well and can tell it the same way every time.
Another way to put volunteer work on your application is to volunteer for something small and then exaggerate about how much you did. For example, a two-hour volunteering session can easily become a three-month-long organizing-and-implementing endeavor by picking the right language and spacing out the timeline of events.
However, if you have a lot of time before sending in your application, actually doing a more long-term volunteer project saves you the trouble of having to think of really creative ways to embellish your accomplishments.