When Jeff left for the final meeting, his hands were empty. Same for when he escaped and hijacked a cab. No way for him to have acquired the briefcase he entered with.
When rescuing Lisa, Jeff made two mistakes that were too dumb for his character. He left the fourth guy behind in the room with the guns when he went to her. Then he left the thugs with all their guns to come after them when he could have tossed or taken them.