I think you could mention something like your first impression to pharmacy field before you entered college and became really interested. Even if it's not too much contact with the pharmacy field, I am sure you had some experience visiting a pharmacy to buy drugs, candy bars, or even milk 😛
Otherwise, if you have any experience related to health care, you can also mention that.
If you don't have that much encounter with pharmacy before college, you can tell the story about how you became interested after college. Just like the post before me said, the best thing to do is pick one or two things that impressed you most during your experience. Either it is from your volunteer, or from your research experience.
Don't worry, I also began my official volunteer in pharmacy the summer before I applied. Trust me, you will observe and learn enough things to write a good essay.
Also, one way that I think could help to make your essay stand out is to pick any current issue in pharmacy today (such as insurance matters, drug price, uninsured patients, etc etc) and elaborate this together with your experience.