Sheets that will actually fit your bed. College beds are often longer than a standard twin. A comforter you won't mind throwing away after four years. Keep the peace with your roommate and neighbors. The more you hang, the less you'll have to attempt to cram in the small college-provided dressers.
Wire hangers take up less room than bulky plastic ones.
A trash can for your room. Clothes you can layer. Temperatures vary widely from halls to classrooms to social gathering spots. The doors there close on their own and you'll want them open to get a breeze and to meet new people. Basically something to do in groups.