I have about half the distance you ride so I just wear whatever I plan to wear to work that day. (with extra shoes and a sweater for excessive A/C left at work) You might not need to change depending on your riding speed and whether its a flat or hilly commute.

I'd go for locks, full fenders, a good waterproof jacket, lights (assuming you will be riding home sometimes after dark), and something to carry your books back and forth in. A rack and panniers would be ideal (look for a pannier that doubles as a backpack for carrying it around campus), but you could get by with a backpack (its just nice to keep the weight and sweat off your back)

For clothes in general think windproof waterproof for outer layers, and comfortable and breathable for inner layers. Dress slightly cooler than you would if you were walking in the same temperatures since you'll generate heat when riding.