"The Future Is Unwritten" is a mix tape that adds up to a shambling musical biography of the late leader of punk firebrands the Clash. (It accompanies the rock doc of the same name that does not yet have a U.S. release date.) It features choice gems from Woody Guthrie, Elvis Presley, Nina Simone and Bob Dylan. There's enough odd or unreleased stuff here to make "Future" a must-have for Clash completists.- The Philadelphia InquirerCDs are rated from zero to four stars, with four being the best.