The full story
Christmas on Knowhere. The Guardians have bought the place from the Collector and taken in Cosmo the Spacedog, and Quill still hasn't gotten over losing Gamora. Kraglin tells the team how Yondu ruined Christmas for Quill when he was a boy among the Ravagers, and that gives Mantis and Drax an idea: get him the best present imaginable.
The two of them head to Earth to bring back Quill's childhood hero, Kevin Bacon. They land in Hollywood, take in the sights, and track Bacon down at his Beverly Hills home, where he is understandably terrified of the two aliens who have come for him. When he tries to run and the police show up, Mantis puts the officers down with her empathic powers, and they take Bacon with them.
Back on Knowhere, the rest of the team, Nebula, Rocket, Groot, Kraglin and Cosmo, throw Quill a surprise Christmas. He is horrified to learn his hero was kidnapped and orders him taken straight home. But aboard the Guardians' ship, the Bowie, Bacon hears how much he inspired Quill as a kid, and decides to stay for the party before he goes.
Afterwards, Quill tells Mantis the rest of the Yondu story: Yondu came around on Christmas after all, and the blasters Quill still carries were his present. Then Mantis gives Quill her own gift, which is the truth. She's his half-sister, another of Ego's children, and she kept it from him for years so as not to remind him of what their father did. Quill is overjoyed.