Labelling potluck dishes was actually standard in my bits of the community back to the early 2000s at larger events, either providing the label for commercial stuff or an index card with ingredients if not.
We didn't necessarily bother for small group stuff (because people's allergies were generally known, and you knew who brought what or it was trivial to ask, because it was 'there are ten people here, all of whom I know, and I know who brought five of the dishes without thinking about it' sorts of stuff.)
I also always tell people if they've got any food limitations, to bring stuff they know they can eat and make sure they have a stash of suitable post-ritual food if needed, because that's just sensible planning.
(I've also been burned a couple of times. The one who sticks in my head was a seeker in the group in Minnesota who I know had been told at least twice that if there were any food limits, to let us know in advance, especially if it affected in-ritual food, and turned up at ritual and said "Oh, by the way, I can't have wine or bread". Which is a thing we can work around if you tell us before that week's grocery run, but 20 minutes before we start ritual is not that time.)
Re: for this comment's purpose, animal products are allergens, because veg*ns. religious stuff also?
We didn't necessarily bother for small group stuff (because people's allergies were generally known, and you knew who brought what or it was trivial to ask, because it was 'there are ten people here, all of whom I know, and I know who brought five of the dishes without thinking about it' sorts of stuff.)
I also always tell people if they've got any food limitations, to bring stuff they know they can eat and make sure they have a stash of suitable post-ritual food if needed, because that's just sensible planning.
(I've also been burned a couple of times. The one who sticks in my head was a seeker in the group in Minnesota who I know had been told at least twice that if there were any food limits, to let us know in advance, especially if it affected in-ritual food, and turned up at ritual and said "Oh, by the way, I can't have wine or bread". Which is a thing we can work around if you tell us before that week's grocery run, but 20 minutes before we start ritual is not that time.)