I'll speak for the distance campuses as to dress code but this may also apply for Gainesville. Depending on what class/event you're going to, you can either dress professionally or casually. Orientation is, of course, professional attire/UF polos. The only class you're required to dress professionally in (for 1PD year) is Pharmacotherapy in the Spring. This is the class you'll eventually wear your white coat to. And going along those lines...any time you are expected to wear your white coat, you dress professionally. Such as screenings/events where you represent UF on or off campus. Any other classes where you're just watching a professor lecture, you can wear jeans/tshirt/normal school attire. Since you will not get your white coat until Spring, the school typically tells you to wear your UF polo and khaki/dress pants.
You will also give several presentations throughout the year in different classes. You will be required to dress professionally when you give presentations.
Use your own judgment as to what would be the best thing to wear. When in doubt...dress business casual with khakis. It never hurts to overdress but looks bad on you to underdress. You'll get the hang of what you can and cannot wear once you start classes and see what other people are wearing on campus.
For the females who don't know what counts as professional: remember 3 B's: no breasts (cleavage), no bellies, no butts. And also don't forget closed toed shoes for labs/screenings when you're dressing professionally. Open toed shoes are fine for class if you aren't interacting with patients.