Charisma Carpenter and James Marsters are known for their roles in two other supernaturally themed shows; Buffy the Vampire Slayer (1997) and Angel (1999).
The character Jenny Klein is named after a writer for Supernatural, Jenny Klein. They both happen to have long blonde hair.
Sam uses the name Agent Sambora when talking to Wendy's sister. Richie Sambora is the guitarist for Bon Jovi.
Charisma Carpenter and James Marsters are the 4th and 5th characters that also appeared in Buffy the Vampire Slayer and spin off Angel. 1st, 2nd and 3rd being Amy Acker, Amber Benson, and Mercedes McNab.
The name of the portable toilet company is BM Disposals. Toilet humour at its best.