One of the best parts of Wonder Woman that was, unfortunately, not used enough was Lucy Davis as Etta Candy. Warner Bros seems to have realized this and are giving Etta some more screen time in the form of an epilogue. Yahoo Movies released a small clip of that epilogue and it could set up a plot point for the Justice League.
— Yahoo Movies (@YahooMovies) August 28, 2017
Etta has gathered Sameer (Saïd Taghmaoui), Charlie (Ewen Bremner), and Chief (Eugene Brave Rock) to send them on a secret mission. They are looking for something "very old and very powerful" that they need to get to the American's.
The most obvious thing it could be is one of the Mother Boxes. We know that the American's have one because we see it in Dr. Stone's apartment in the trailer. It'll be a really fun way for them to connect the two movies in a subtle way instead of beating people over the head with it. Perhaps someone will mention this mission in Justice League to Diana and she'll see who it was. Even if it's just a name or a picture or just seeing Etta's signature on something. Diana would know and it would be a quick and easy way to connect those movies.
Summary: Before she was Wonder Woman she was Diana, princess of the Amazons, trained warrior. When a pilot crashes and tells of conflict in the outside world, she leaves home to fight a war to end all wars, discovering her full powers and true destiny.
Wonder Woman, directed by Patty Jenkins, stars Gal Gadot, Chris Pine, David Thewlis, Robin Wright, and Connie Nielsen. It'll be available on VOD tomorrow and on Blu-ray on September 19th.