You'll see blood. Lots of it. Lots of vomit, stool, sputum -- any body fluid you can think of. And don't get me started on the varying forms of stench.
The good news is, you will get over it. I'm a former sympathy vomiter (oh, you're vomiting? me too) who threw up twice on my first day of med-surg clinicals. My classmates found it hilarious until it was their turn. At least I wasn't the one who fainted. Seriously, you do get over it. Don't let a phobia stop you from pursuing a great career. (Most do get over a particular fear, but if you don't, you'll often find a colleague who's willing to step in for you; after all, s/he has probably got a phobia of her/his own.) If anyone had told me that I would one day drain the sputum from a patient with a perforated esophagus without batting an eye, I'd have laughed. But I can do it now, and so can you.
No, you don't get to choose your clinicals. We had to observe in OR on two occasions. On the yuck scale, wound care is far worse than OR.