The Atlanta Panhellenic Council holds monthly meetings and our alumnae chapter sends a Delta Zeta delegate to attend and report back on what's going on. Last year, the majority of NPC sororities in the Atlanta area worked together on a big charity event for the Make A Wish Foundation. It was a Bring A Bachelor Event, and was hugely popular.
Another thing that our Panhellenic Alumnae chapter does is help match up recent high school graduates with alumnae members so that the girls can get recs for Rush when they enroll in college for the next fall.
I know that our organization does other things, but I can't think of them right offhand. If anything else crosses my mind, I'll edit this post and add them.