flying_babyb, since you're a college student that rents, you just have to organize what you have.
In all of my college days I never once put books in my closet. I always ALWAYS had at least one bookshelf, and let's be honest, once I got out of the dorms I had at least 2 smaller bookshelves. Once I hit chiropractic school and was in my "motel 6 suite" style apartment (the bedroom/bath/vanity looked just like a little motel room, but then it had a living room/kitchen tacked onto it) I had about 4 bookshelves. If it had ONLY been the bedroom area, I actually could have fit my stuff in; it would have been crowded, but with the bookshelves lining the walls I would have been fine.
So bookshelves are definitely important.
As for clothes, I've never been the type to get rid of stuff. I was wearing bright pink low-heeled shoes from my 8th grade commencement for at least 10 years. And when I have donated stuff that I liked based on the "if you haven't worn it in x amount of time" theory, I inevitably deeply regret it later. So I won't tell you to do that, b/c I don't believe in it for some personalities.
I'll also mention that space bags do NOT clear up a lot of space. In fact I think the room my space bags are taking up is MORE than what the items inside were taking up before. They are big, bulky, have to be accessible b/c they have to be re-vacuumed every so often. You can't store them in certain ways or you'll damage them, etc. I wish I'd saved my money to get the new cubes instead, b/c maybe those are better. But the non-cube ones aren't giving me lots of space, they are just taking up new space!
When you move, if you're in a roomie situation, try to work with the roomie to carve out some space outside of bedrooms. It's always nice, and more family-like, to have bookshelves in the living room, so that things are easy to grab to study on the couch. And it just looks cozier. My junior year of college I lived with 3 other women that I rowed with, and two of us were in nearly the same major so having our books together was nice. Duplicate books of course, but still kind of fun. If I'd had to keep all my books in my room it would have been a bit sad. You do have to TRUST your roomie for that, of course.
Good luck in organizing!