Problems with Packing

How do you pack for a whole year of your life? When I went to Scotland for a semester, it wasn't so bad, and I actually had two cases because I had one of my parents who could claim the other case as theirs when we went to and from. But now it's just me, taking enough stuff to last me a year in a case that can't weigh more than 50 lbs. HOW? I've also got a small carry-on, and my bookbag, but that's not enough! I've got a full case already, and I still have more things I want to put in! Not just clothes, but what about all my toiletries?? And I can't find my favorite sweater! I don't even know what to do right now. I have to repack it in the next week before I go to Chicago, but at least I have an idea of what I have at least. I may have to leave some of my scarves behind... I guess I'll manage.