Whatever was in the shoebox that is labeled "Cincinnati", in the movie Hot Tub Time Machine, was never revealed to the audience. Many people think this could be a lead-in to a sequel.
Hot Tub Time Machine is a 2010 comedy film directed by Steve Pink and stars John Cusack, Rob Corddry, and Craig Robinson. The movie has been described as a mash-up of Back To The Future and The Hangover. It is about four men, who travel back to the 1980's in a time-shifting hot tub and the hilarity that ensues.