It totally depends on the rotation and the residents and attendings you are working with. It also depends on what the hell you mean by "presentations."
Some clerkships have required PowerPoint presentations (15-20 min) during weekly student didactics. Some clerkships have absolutely nothing. And most are in the middle, where from time to time you have to talk for 5 minutes about some topic that the resident or attending wants to know about, and it is usually prudent to make a 1 page hand-out with a few references. I had one rotation where one attending was notorious for asking med students to do "two minutes on topic X tomorrow" whenever they said anything stupid (I proudly made it through the month without giving a talk). But it is not predictable -- so ask people from your own medical school.