There is a statement in the closing credits: "No raccoon or tree creatures were harmed during the making of this movie. However the same cannot be said for the handlers of the raccoon and tree creatures."
Several credits in the closing credits read "I am Groot" before flickering and changing to the actual credit.
At the end of the credits the disembodied head of Zardu Hasselfrau states: "In these times of hardship, just remember: We are Groot!"
Cosmo the dog (from the first film), Howard the Duck and Jeff Goldblum are seen in the credits
SPOILER: There are 5 scenes in the closing credits:
The opening credits are of Groot dancing to Star-Lord's music, during a battle between the Guardians and a space monster (seen in the background).