Damien Darhk's mask collection from top to bottom: Ragman, Black Canary, Wild Dog, Vigilante, Green Arrow, The Flash, and Spartan.
Rip Hunter's cakes contain references to Arthur Darvill's previous role as a companion on "Doctor Who". One is topped with a bow tie, referencing the signature fashion item of the Eleventh Doctor. Another is composed of antique clock faces similar to those featured in the Twelfth Doctor's opening credits sequence.
Snart and Rory talked about being put into prison and make escape plan, "just like the old times". Probably intended as a Prison Break (in which they are the main characters) reference.
When Leonard Snart (Wentworth Miller) and Mick Rory (Dominic Purcell) are talking about how "they're the kings now", Snart says "I can get us thrown back in Iron Heights, stage a breakout, just like old times". This is a reference to the shows Prison Break (2005) and Prison Break: Sequel (2017), in which Miller and Purcell star as the protagonists Michael Scofield and Lincoln Burrows, and break out of several prisons.
The building Thawn is housing his reactor in resembles the design of the headquarters of the Legion of Doom from Super Friends (1973).