A suitcase containing money was in the possession of Emmett Brown. He pulled it out of the DeLorean time machine upon arriving in 1955 with Marty McFly. It contained various amounts of dollar bills from different eras, allowing him or Marty to purchase items in almost any time period. Bills from 1861, 1863, 1875, 1914, and 1917 were present in the case.
Doc pulled out a $20 bill that would have been used in the 1950s which allowed Marty to purchase a black trilby hat and black leather jacket as an 'inconspicuous' disguise.