This is a feature request. If I'm signed up for a session, I'd like to have a text field for private notes about the session which I can see along with the session info as part of my schedule, but which aren't shown to anyone else.
Or, in user story form:
As an attendee
I would like to be able to store a few sentences of notes for my own use about a session
So that I can manage session-specific details (costuming, masking, etc.) alongside my schedule.
If that seems interesting, I'll try to make a pull request for it.