Juliet Landau didn't have to audition for the part of Drusilla. Joss Whedon had been very taken by her performance in Ed Wood (1994) so she was offered the part within an hour of meeting with Whedon.
Spike, promising to kill the slayer, says, "I'll chop her into messes". He is not refering to an untidy, sloppy condition. 'Messes' is an old English term for food (especially meat) cut into small pieces, and later for food in general. Military dining halls are still called 'mess halls'.
When Sheila asks Buffy if she really burnt down a building one time, Buffy replies "Not exactly one time", referencing when Buffy was involved in the burning down of an abandoned science building in Some Assembly Required (1997).
In the original script, Spike's car was intended to be a Cadillac. In reality, it is a Desoto Sportsman, California license plate number HIA-873.
Xander's line was cut from the original script for length: "The important thing in punch is the ratio of vodka to schnapps.... That was obviously far too sophisticated a joke for this crowd."