Nebula and Open (to multiple threads)
Nebula had decided to attend the celebration for several reasons.
One, it was the birthday of Captain Rogers, a person who deserved to be celebrated for so many reasons, including the five years she had memories of where he and Romanoff had held things together after half the population in the universe had been wiped out by Thanos.
Two, it was an opportunity to socialize with and outside of her usual group. Most of the people at the celebration would only see Loki's illusion spell and she'd be just another happy citizen consuming hot dogs and beer. It was a breed of 'normal' with which she wanted more experience.
And three, Barnes might be there and they could just happen to meet and possibly share some time together. 'What a surprise to see you here?' she could say. Even as she thought it, she was disgusted with herself. How utterly lame could she be?
She had dressed casually for the occasion, right down to having a little flag of the nation. Mostly, she kept it sticking out of the back pocket of her jeans, except when she sat at one of the picnic tables or on the grass to look at the water. Then she would stick it between the table planks next to her plate or in the ground beside her, respectively.