Natasha, of course. She wore the hat. She hates it, but she hates upsetting Morgan more so she kept it on for a little while. At LEAST until it was acceptable to take it off. Probably when someone else mentioned it. I have to hit up Meg, but it's possible she showed up with that Buck.
Carol arrived and wore the hat the WHOLE TIME. Fight her if you make fun of her. She will ask where your festive spirit is. Does Morgan wanna be Sargent Fun? :D
Nebula was there. She kept the hat on until Morgan was not around, then took it off. Whenever Morgan looked at her again, she'd put it back on and pretend she'd never taken it off.
IDK if Aphra's invited but she works with Tony as The Googler, a title she enjoys. If so, she would not have worn the hat because she already has one on, see? It's festive!
IDK if Rey invited Margo.
Shuri there? If so, she did some fancy origami on the hat and made it fit her outfit.