The phrase was first used in songs by artists such as The Beatles and shortly after by Simon & Garfunkel. This phrase has absolutley no definitive meaning given by dictionaries or artists such as John Lennon who first used it. The phrase has two other widely known spellings: goo goo g'joob and coo coo ca choo. It is believed to be used in songs and in 60s and 70s slang as a phrase left to be freely interpreted by anyone based on the surrounding context it is used in. The freedom to betsow any meaning upon the phrase makes it a statement about freedom of expression, which is a meaning in itself.
A widely accepted variation of the meaning is a slang way to assure the state of things is entirely fine; an expression of reassuring goodness.
In "That '70s Show", Donna Pinciotti said coo coo ca choo as an end to a random string of rhymes while stoned.
Man, you been a naughty boy, you let your face grow long.
I am the eggman, they are the eggmen.
I am the walrus, goo goo g'joob.
--The Beatles' "I Am The Walrus"
Hide it in a hiding place where no one ever goes
Put it in your pantry with your cupcakes
It's a little secret, just the Robinsons' affair
Most of all, you've got to hide it from the kids
Kookookachu Mrs Robinson
--Simon & Garfunkel's "Mrs. Robinson"
"Everything is all right." "No worries." "All is good."