Hi Stephanie. If you mean what classes as an undergrad, you don't need to worry too much about targeting specific classes/activities to surgery itself. It is much more important to fulfill the general undergrad requirements for getting into a "good" medical school (doing well in your pre-med classes, MCAT, etc). Often people graduate with a B.S. degree in Biology, since once you do the required pre-med classes (chemistry, biology, basic physics) you are often most of the way there already. But not necessary at all.
Of course, if even as an undergrad, you (for example) start doing research in a surgical lab and then present yourself to medical school admissions as someone who has a clear calling for surgery, that may look good. But not something to worry about. Note that many *medical students* are completely confused over what they want to be for the first few years of med school.
Specific example: my brother completed his neurosurgery residency at Stanford along with a bunch of awards and notable papers. In medical school however he seriously considered pathology and psychiatry before deciding on surgery. As an *undergrad*...well, he was more interested in philosophy, religion, and English literature than anything else...although of course he did well enough in his pre-med classes.