According to Brandon Routh on Twitter, the "bulletproof coffee" Cat mentions in this episode was used by writer Andrew Kreisberg after Routh's "obsessive" use of the term. Routh, of course, played the title character in Superman Returns (2006) and stars as The Atom in Arrow (2012) and its spin-offs.
Cat Grant (Calista Flockhart) titled her article "Millennial Falcon". In real life, Flockhart is married to Harrison Ford, who played the Millennium Falcon's pilot Han Solo in Star Wars: Episode IV - A New Hope (1977) and its sequels.
Kara says to her sister, "Do not watch Homeland (2011) until I get back." Melissa Benoist guest starred in Homeland (2011) during its first season as Stacy Moore. David Harewood also appeared on the series as David Estes.
The couch scene between Alex and Kara was a natural scene between Chyler and Melissa. Kara throwing the pillow at Alex wasn't scripted, Melissa did it on the spot, as was Chyler's reaction.
The real demon core was a sub-critical sphere of plutonium used in nuclear weapons development during World War 2. In reality, partially surrounding such a sphere with a neutron reflector (especially partially surrounding it, as it was with Supergirl's hand) would have actually *increased* the radioactive output and caused it to go critical, emitting large doses of radiation and killing Jimmy Olsen. This happened twice, accidentally, to the real demon core, which resulted in the death of two scientists and the poisoning of several other Manhattan Project personnel.