Mine aren't in college yet but here's something from when I was:

My father insisted on engraving all my electronics with my SSN. Nothing ever went missing but some of my books did. After the first one disappeared, I wrote my name on a certain page number in the rest of my books and when another went missing, I went to buy a new copy and the guy handed me my own book back! I could prove it because of my name being in it. I'm not sure whether it was my roommate (who was rarely in the room, I think she pretty much had another place) or her friends, they may have been given the key.

Since you don't know the kid(s) he'll be rooming with, it might be a good idea to invest in a small safe if he has anything small and valuable that would be left in the room when he's gone (meds, documents, etc). And if you haven't had the credit card talk yet, that might be a good idea. I don't remember ever signing up for anything (even for freebies) but when I came home from school on a break, I somehow had a credit card statement ($0 balance) without ever getting the card.