Ask the people attending to bring a small gift for each of the participants. Last time I went to a retreat, I made little bags from fat quarters for the attendees. I basted them so they could easily be taken apart and used later. It was something to put small 'stuff' in to carry around.
We were from an internet group so we didn't really know each other. Of course we had a prize for the best name tag.
It was one of my favorite weekends ever!