Clinical nurse specialist

Hi everyone. My unit manager in Emergency department has approached me and wants me to become a clinical Nurse Specialist. This is great but I am after some suggestions on areas that people would think would be good to specialise in. My unit manager has some suggestions but I'm not really taken by any of them at this point and thought others may have some suggestions
What would a clinical nurse specialist do for you in your current position? I would think that for your benefit long term, a certification in critical care nursing, trauma nursing or emergency nursing would be in your best interest.But that would make you more marketable as an emergency department nurse. And that may be where this is coming from.Best wishes!