When Oliver breaks into the federal prison, he maintains radio contact with Lyla using her code name "Harbinger." In DC comics, Harbinger was the superhero persona of Lyla Michaels who was trained by "The Monitor" as a Guardian for the Multiverse.
The Briefcase that the man drops at the start of the episode says Kord on it, a reference to Ted Kord, the first Blue Beetle. This might mean that we could see the Blue Beetle in the Arrowverse.
Diggle is supposed to be in cell 1138. The number 1138 is a running Easter egg in the Star Wars films after George Lucas' first film THX-1138. Among the references in Star Wars is Chewbacca pretending to be a prisoner transfer from cell block 1138 in New Hope
The IP address for the dark web dead drop (108.166.7.161) leads to cwtv.com.