Jack is drinking. Quite a bit. If you ask why he's going to tell you it's because this is part of his character, but really he's kind of stressed for a variety of reasons (including a TASK he must accomplish??? he has to warn Raine about Enoch??? what if he laughs???). Jack thinks he'll be more fun and successful if he's buzzed.

He's making rounds of the room with a drink in his hand and a persona-appropriate song in his head in case of accidental touches (this is Jack accepting the subtle L of being a philanderer).