On October 21, Pepsi Cola will reap the rewards of a 25-year-old product placement with 6,500 limited edition bottles of Pepsi Perfect – a fictional soft drink featured briefly but prominently in 1989's Back to the Future 2. October 21 2015 is the day that the movie's main character Marty McFly travels forward to in time, and fans are preparing to honour the date accordingly.
American entertainment company Universal Pictures also made use of its connection to Back to the Future by releasing a spoof trailer for Jaws 19 as advertised in the film's fictional 2015. German car maker Mercedes-Benz is also getting into the holiday spirit without any immediate connection to the time-travelling trilogy, as is Japanese automaker Toyota, alongside the film's original lead actors Michael J Fox and Christopher Lloyd.
Back to the Future is not the only fictional world to inspire real-life landmark days. Seinfeld fans may celebrate the Christmas alternative Festivus, Harry Potter readers flock to London's Kings Cross train station on September 1 for the start of a new school year at Hogwarts, and Star Wars fans mark May the 4th (be with you) in their calendars. The built-in enthusiasm of existing fan bases make secular pop-culture holidays a great chance to connect with the large audiences that observe them.
To keep up with developments in pop culture, follow our Pop-Culture Round-Ups. For more on the impact of fan culture, see Tribes and Fandoms. Finally, see Comic Con International 2015 for our coverage from the biggest pop-culture celebration of them all.