How do I see who's attending a feast?
Solution 1:
This is super unintuitive, but when you host a feast, a little tiny feast icon generates on the map when you're zoomed in close enough. I think it's always in your capital when you host it, but if you get invited to a vassal's feast, it'll be in their capital instead.
When you click it, you get a nifty little pop-up with a list of all the persons attending!
Hunts and pilgrimages also generate a tiny location-specific icon, but I don't think those expand out to show who's with you. (This may be a bug)