I'm a born and raised Los Angeleno who opts for public transpo.
The great thing about Keck is that they have a free shuttle service to the main campus or to Union Station, which is a transit hub. From this hub, you can catch trains out to Pasadena and Hollyweird. There's more public transpo options than you might imagine.
If you buy a nice road bike, you can jam down Sunset Blvd/Cesar Chavez to Echo Park or Silver Lake, recently gentrified communities, where you'll find plenty of skinny pants/asymmetrical hair cut types. You can probably bike to these communities from Keck within 30 minutes. Or you can just live downtown, which is close.
USC is comprised of a main campus and health science campus but you'll be spending most of your time at the health science campus. Once you start doing clerkships, it may get cumbersome to get around but you'll be able to pull it off. I'd buy a hog. In California, it's legal for motorcycles to take the carpool lane and lane split.