How often are you talking about?
We have all-camp activities in the evenings a few nights a week. Traditional activities like you mentioned, campfires, round robins of activities/games/crafts/etc...
One of the years I was assistant camp director, we had an occasional ad staff evening activity night. We made a rough schedule and sent it out to the units beforehand. Any ad staff member who wasn't on duty that night, or off, would lead an activity for anyone who wanted to participate. There was Capture the Flag one time, and kickball, and sidewalk chalk drawing, and floor hockey... And not a lot of kids showed up to all of them, but it was fun and gave them more options if there wasn't much in the unit's schedule that night.
