The 5 trick-or-treaters at the start of the film foreshadow the road trip locations yet to be visited: a pirate (Jean Lafitte) for Isle Grande Terre, Louisiana; a witch (Martha Corey) for Salem, Massachusetts; a gangster (John Dillinger) for the Little Bohemia Lodge in Manitowish Waters, Wisconsin; a ghost (Sarah Winchester) for the Winchester Mystery House in San Jose, California; and a cowboy (Billy the Kid) for Stinking Springs, New Mexico.
In the basement ghost scene, the name "William" is called out by an unseen woman; this is meant to be the ghost of Sarah Winchester calling out for her husband.
The belt buckle found at the bottom of the lake is inscribed with the initials "JD" for John Dillinger, a gangster who is meant to have lost his luggage during a firefight at the nearby Little Bohemia Lodge.
When Oliver and Veronica walk past the famous Winchester Mystery House, a tour guide is explaining how Sarah Winchester's jewelry was worth only its weight in gold; the woman had pried out all of the gemstones, presumably with a supernatural intent. This explains the bag of loose jewels later discovered.