April Kepner and Miranda Bailey are vocalizing 'Scotland the Brave', a Scottish patriotic song that is a traditional funeral piece.
Meredith says, "this is your brain on drugs" which is a very obvious nod to the anti-drug ads from the eighties ending with the same phrase.
Judgment Day is a song by Stealth, released in 2017.
When Schmidt is running back to the OR with Webber's cancer detector" pen, the family stops him to talk. The little girl then refers to him as Dr. Smith and not Dr. Schmidt.