As James Gunn's farewell to Marvel, Guardians of the Galaxy Vol. 3 brought a perfect conclusion to the journey of this lovable band of misfits. However, this ending also laid interesting groundwork for the future, which is worth exploring...
This article contains absolute spoilers. Please read with discretion.
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At the end of Guardians of the Galaxy Vol. 3, "Star-Lord" Peter Quill returned to his home on Earth to reunite with his grandfather; Mantis decided to embark on a journey of self-discovery; Drax and Nebula remained in Knowhere, continuing to lead its people; Gamora rejoined the Ravagers; and Rocket, at the urging of the Guardians, became the new captain, leading a brand new cosmic team.
Scene 1: The New Guardians of the Galaxy
The first post-credit scene reveals the members of the new "Guardians of the Galaxy" led by Captain Rocket: Groot, Cosmo the Spacedog, Kraglin, Adam Warlock, and a young girl named Phyla.
The group is on a desert planet, listening to the Walkman Quill left for Rocket, discussing their favorite singers. Rocket ultimately chooses "Come and Get Your Love," the song Star-Lord was listening to in his first appearance, bringing the entire trilogy to a perfect full circle.
In the main story of Guardians of the Galaxy Vol. 3, Phyla is one of the High Evolutionary's imprisoned test subjects. However, in the official comic canon, Phyla's full name is Phyla-Vell, and she is the daughter of "Captain Marvel" Mar-Vell. The film does not mention the surname "Vell" for now. Perhaps the character's setting has already diverged significantly from the original source.
The actress playing Phyla is newcomer Kai Zen, a Japanese-American child star who debuted on the Disney Channel. She began her career in 2020 by voicing characters in Disney cartoons, and her live-action works include the 2020 film Feel the Beat and the 2022 film Chip 'n Dale: Rescue Rangers.
Besides Phyla, another new member, Adam Warlock, was saved by Groot, his original target. This led him to understand the meaning of "everyone deserves a second chance," as he put it, and with this profound realization, he joined the Guardians of the Galaxy as a new team member.
Scene 2: Quill's Return to Earth and His Grandfather
In the second post-credit scene, Quill returns to his home on Earth and reunites with his grandfather. The opening of the first Guardians of the Galaxy film showed Quill, accompanied by his grandfather, visiting his dying mother for the last time. Unable to accept his mother's death, Quill ran out without looking back and was subsequently taken into space and adopted by Yondu.
This film reveals for the first time that his grandfather's full name is Jason Quill. In the official comic canon, Jason is Quill's middle name (Peter "Jason" Quill).
Star-Lord's grandfather is played by Gregg Henry, an actor who is also a long-time collaborator and regular cast member in Gunn's works. His presence can be seen in films directed by Gunn, including Slither and Super. 
His grandfather reminisces with Peter while reading a newspaper. The news on the back of the newspaper, "Kevin Bacon reveals alien abduction," refers to the plot of The Guardians of the Galaxy Holiday Special. Kevin Bacon's still from that film also appears in the end credits.
Further Reading:
The Guardians of the Galaxy Holiday Special: 26 Easter Eggs and Details Explained!
Guardians of the Galaxy Vol. 3: 17 Most Important Easter Eggs and Details Explained! These Arrangements Were for the Fans!