Our chapter meeting attire was casual... it pretty much boiled down to, "wear clothes". People showed up in anything from business-casual to jeans and t-shirts.
My freshman-year roommates, who were in other sororities, had calendars that listed out dress codes for their chapter meetings. I think they were a little jealous when they had to wear dresses and I was headed to chapter in my jeans
In retrospect, though, I wish we'd had some sort of dress code, even something as simple as "no jeans". When you're wearing formal or even business-casual attire, you feel and act more professional, and it's a reminder that it is a
business meeting.