I have missed a lot of NCIS, but I am wondering if it was ever disclosed what was in the briefcase that Gibbs gave Abby, which was a gift to her from him. They only showed her open it and a gold glow shine onto her face, but did not say what it was.
It was a MacGuffin. As Abby notes:
This is so 'Pulp Fiction'
A reference to a similar glowing briefcase used by Quentin Tarantino in Pulp Fiction.
It's contents are not meant to be known, because what it actually is or does is pointless to the plot. In many cases, the mystery of the item helps keep the audience interested, as the item may not live up to the hype.
There has never been a reference to the gift again.