For your reference, we've listed out every Double Steak Day celebration dating back to the holiday's creation and extending forward until we got kind of bored!
 

 

December 19th, 2004. 1st Double Steak Day
December 18th, 2005. 1st Intentional Double Steak Day
December 17th, 2006. 1st Strangers Celebrate Double Steak Day
December 16th, 2007. 1st Vegetarians Celebrate Double Steak Day
December 14th, 2008. Mascots "Lunch" and "Dinner" Debut
December 13th, 2009. DoubleSteakDay.com Goes Live
December 19th, 2010. Status Quo Expertly Maintained!
December 18th, 2011. Official Sponsor of Occupy Two Steaks Movement
December 16th, 2012. 1st Double Steak Day Tweets #dsx2 #fullnow
December 15th, 2013. 10th Anniversary! Hope you didn't eat a tin steak!
December 14th, 2014. The great rules convocation. Watch this space.
December 13th, 2015. New rules! No more 3rd Sunday DSx2s!
December 11th, 2016. Now on Facebook!

December 10th, 2017.
December 9th, 2018.
December 8th, 2019. Earliest Double Steak Day yet!

December 13th, 2020.
December 12th, 2021.
December 11th, 2022.
December 10th, 2023.
December 8th, 2024.
December 14th, 2025.
December 13th, 2026. DSx2 time capsule opened to reveal 2 steaks!
December 12th, 2027.
December 10th, 2028.
December 9th, 2029.

December 8th, 2030.
December 14th, 2031.
December 12th, 2032.
December 11th, 2033.
December 10th, 2034. 1st Robots Celebrate Double Steak Day
December 9th, 2035.
December 14th, 2036.
December 13th, 2037.
December 12th, 2038.
December 11th, 2039.

December 9th, 2040.
December 8th, 2041.
December 14th, 2042.
December 13th, 2043.
December 11th, 2044. 1st Double Steak Day on Mars
December 10th, 2045.
December 9th, 2046.
December 8th, 2047.
December 13th, 2048.
December 12th, 2049.

December 11th, 2050.
December 10th, 2051.
December 8th, 2052.
December 14th, 2053.
December 13th, 2054.
December 12th, 2055.
December 10th, 2056. 1st DSx2 in Iambic Pentameter
December 9th, 2057.