What was Kesey's group of friends called?

It is the birthday of Ken Kesey (1935), who is remembered for his novel One Flew Over the Cuckoo's Nest (1962), a drama set in a mental institution. It received great acclaim, and was adapted as a movie. When he had to travel from California to New York for the publication of his second book, Sometimes a Great Notion (1964), Kesey's friend, Beat writer Neal Cassidy, arranged for a cross-country trip on a psychedelic-painted school bus. Do you remember the name of the group of hangers-on who went on the trip? Who wrote a 1968 book chronicling the events of the trip, and what was the name of the book? Enter your answers below.