Facebook definitely - events, chat, I don't think I need to explain the benefits of FB.
Whatsapp, good for group chats especially.
Yik Yak, good for anonymous uni discussion.
Snapchat, to a lesser extent. Why is snapchat needed? I'm not totally sure myself, but I use it. Concerned about privacy? Do what I did, accept random friend requests from 1-2 strangers who just send dick pics. That's a good reminder not to put anything up you'd care about being on the front page of a tabloid.
Google isn't really a necessity in social media terms, though document sharing can be useful.
If you're working in a field where confidentiality is involved (healthcare being the main one I can think of where it'll be an issue during the course), Wickr is good, it's a more secure snapchat.
I disagree about LinkedIn being required, I haven't used that at all in my life, despite entering as a semi-mature student and coming from a business background. I guess maybe if you're job-hunting, but that depends on the field. Certainly any jobsearching mid-degree is unlikely to be helped much by LinkedIn.