Re: OOC - Check in!
I'm not creative right now, but:
Marcus came with Jyn.
Clint came with Natasha. Like I said in my comment to Jeanne, he is not missing the opportunity to celebrate with Star Wars heroes.
Edmund came, probably with Reyna. He and Cassian have been on missions together and were army buddies in Breck.
Mordecai also came - figuring he's gotten to know Cassian through Mara. He came alone and enjoyed the casino theme.
Ferris is on one of Cassian's teams, so he would come.
All of them would have brought gifts. I'm not very creative right now, but Edmund's tend to the thoughtful and homemade. Mordecai is overly generous, but will probably offer alcohol on this occasion. Marcus is a bit of a troll, but usually only with close friends.