Powdered coffee lightener, no doubt.
That was the joke going around. Apparently, a stewardess pulled open a drawer in the galley and a bunch of white dusty powder flew out on her. We didn't know this until later. We were sitting on the plane for quite a while then I looked out the window and saw security and a firetruck pull up behind the plane. A bunch of officials climbed up the stairs to the cockpit and after a while we were told to leave the plane. They said we would be contacted later if necessary.