Jack Daniel's is a brand of Tennessee whiskey produced in Lynchburg, Tennessee, by the Jack Daniel Distillery, which has been owned by the Brown–Forman Corporation since 1956.
Many of the Family Guy characters have been seen drinking from bottles intended to evoke the brand, but it has also been clearly identified on several occasions:
Peter needs help from 'Jack Daniels' before confronting Lois over Chris' report card in "If I'm Dyin', I'm Lyin'".
Glenn Quagmire needs to fly though a billboard for Jack Daniel's before being able to fly though another one of Greta Van Susteren's crotch in "Mother Tucker".
Wild West uses Jack Daniel's to treat his wounds in "Old West".