There was no Jack Dawson, Rose DeWitt Bukater (or Rose Calvert, Rose Dawson Calvert), Ruth DeWitt Bukater, Caledon Hockley, Trudy Bolt or Spicer Lovejoy on the real Titanic.
There are numerous passenger lists avalible for viewing online and not in any of them will you find any of those above mentioned names. You might find a Jack or a Ruth, but I've never seen a Rose, Trudy or Spicer during the times that I've ever looked up a passenger list. They were fictional, made up, did not exist on the real Titanic.
Cameron got some of the names from and/or the characters were based upon:
The name of the character Caledon Hockley derives from two small towns (Caledon and Hockley) near Orangeville, Ontario, Canada, where Cameron's aunt and uncle live.
Old Rose was modeled after 103-year old sculptress Beatrice Wood of Ojai California
When James Cameron was writing the movie, he intended for the main characters Rose DeWitt Bukater and Jack Dawson to be entirely fictitious. It was only after the script was finished that he discovered that there had been a real "J. Dawson" who died aboard the Titanic. This "J. Dawson" was trimmer Joseph Dawson, who had been born September 1888 in Dublin, Ireland. His body was salvaged and buried at Fairview Lawn cemetery in Nova Scotia with many other Titanic victims. Today, his grave stone (#227) is the most widely visited in the cemetery.
The characters of Jack, Rose, her mother Ruth, her fiancee Cal, his bodyguard Spicer, Fabrizio, and the treasure hunters are all fictional creations of James Cameron. They are not based on any real people but rather are dramatic representations of the rich and poor people on the Titanic.
There was a J. Dawson among the crew who is buried at the Fairview Lawn cemetery in Halifax, Nova Scotia, Canada. However, his first name was James and his existence was unknown to Cameron when he wrote the "Titanic" screenplay. This fact does not deter hundreds of movie fans from leaving flowers and notes at the gravesite. I approve of the misunderstanding because it helps remind us of the plight of the real victims of the Titanic.