The Grateful Dead: Phil and Jerry, the brownie-eating 1970s hippies, seem to be references to Phil Lesh and Jerry Garcia of The Grateful Dead.
Rosie may be a reference to the reoccurring symbol of roses in Grateful Dead songs and art. In the Grateful Dead "Ramble On Rose", the protagonist's name is Rose.
Also, the name of the band Grateful Dead has been attributed to this quote from the Egyptian Book of the Dead: "We now return our souls to the creator, as we stand on the edge of eternal darkness. Let our chant fill the void in order that others may know. In the land of the night the ship of the sun is drawn by the grateful dead."