Patti Forte, Will Forte's real-life mother, played Patti Miller in the premiere episode "Alive in Tucson". Patti Miller was the mother of Phil Miller, and was shown during a flashback on one of Phil's past birthdays. In the show, she was explained to have been killed by the virus.
In season one, episode seven, "She Drives Me Crazy", Carol (Kristen Schaal) is stuck with a cow in her house that won't go down a staircase. The same thing happened on Bob's Burgers (2011) season one, episode three, "Sacred Cow", also starring Schaal.
In season one, episode six, "Some Friggin' Fat Dude", Melissa mentions that The Shawshank Redemption (1994) is her favorite movie. She later mentions The Godfather (1972) is "like my second favorite movie". Those are the top two rated movies in the IMDb top 250 movies of all time.
The trivia items below may give away important plot points.
In season two, Will Ferrell guest starred as Gordon. We later found out that Gail (Mary Steenburgen) dated him in the show. Steenburgen played Ferrell's stepmother in Elf (2003), as well as his mother in Step Brothers (2008).
There's been a recurring gag ever since the beginning of season two, where a famous guest star is brought in and is killed off almost immediately with only one line of dialogue: -Will Ferrell, as Gordon (season two, episode two) died from a heart attack after being scared by Carol. -Jon Hamm, as Daryl (season three, episode one) was shot and killed by Melissa. -Jack Black, as Rear Admiral Roy Billups (season four, episode one) was shot and killed by Pat.