Well, Bernie's already said he has no interest in nationalizing heavy industry as was contemplated in the mid 20th Century. In Finance it's insanely complicated, since assets are diverse and in many ways non-material (typically one is buying alleged acumen and stability, not physical resources). For example, I don't know how one would go about nationalizing banking.
The obvious first step is to break up any institution that is too big to fail and restore effective measures to prevent (and punish) collusion. Changing the legal code to impose real criminal penalties on white collar criminals would help as well -- after all, without deterrents they'll still steal. And the overall change of direction of capping wealth at only disgusting rather than ludicrously disgusting levels would at least diversify the criminal field and get them fighting against (and ratting out) each other.
How do you go after any Mob? Give the small fry immunity to testify, throw the big fish away for life, and close down the inter-generational conveyor belt that keeps producing one cohort after another of well-conditioned crooks. That would about wrap it for the Eight Schools Association.