Venus on the Half Shell — Philip Jose Farmer

Simon Wagstaff narrowly escapes the Deluge that destroys Earth when he happens upon an abandoned spaceship. A man without a planet, he gains immortality from an elixir drunk during an interlude with a cat-like alien queen. Now Simon must chart a 3,000-year course to the most distant corners of the multiverse, to seek out the answers to the questions no one can seem to answer.