I just posted a thing in my own journal that includes a brief mention of my harpfamily making Stone Soup every year at our annual retreat. I'm not sure whether it ever included an actual stone, but the 'everyone brings something to put in the pot' type of thing. Now there's so many dietary restrictions that we can't do that anymore, but we still make (really good) food for each other (just without the central symbolic dish that you'd feel left out if you couldn't participate in).

Hm... or situations like con-friends/families? The people that you only ever see at this one event (or series of events)...