The song that Slim Slavey and the Slavers are playing is, Run, Shaker Life by Richie Havens (1968).
Mr Big were a British pop rock band, active in the 1970s and 1990s. They were formed by Jeff Pain (aka Dicken) and best known for their 1977 Top 5 hit, "Romeo". The band was originally active from 1972-78.