The phrase E ticket refers to an unusually interesting, thrilling or expensive experience. It derives from the admission ticket

Ticket (admission)

A ticket is a voucher that indicates that one has paid for admission to an event or establishment such as a theatre, movie theater, amusement park, zoo, museum, concert, or other attraction, or permission to travel on a vehicle such as an airliner, train, bus, or boat, typically because one has...

 system used at Disneyland

Disneyland Park (Anaheim)

Disneyland Park is a theme park located in Anaheim, California, owned and operated by the Walt Disney Parks and Resorts division of the Walt Disney Company. Known as Disneyland when it opened on July 18, 1955, and still almost universally referred to by that name, it is the only theme park to be...

 and Magic Kingdom

Magic Kingdom

Magic Kingdom Park is one of four theme parks at the Walt Disney World Resort located near Orlando, Florida. The first park built at the resort, Magic Kingdom opened Oct. 1, 1971. Designed and built by WED Enterprises, the park's layout and attractions are similar to Disneyland in Anaheim, California...

 theme parks before 1982, in which the E ticket (officially termed "E coupon") admitted the bearer to the newest, most advanced, and/or most popular rides and attractions.
When Disneyland opened in 1955, visitors purchased an admission ticket to the park at Main Gate booths, then purchased separate admission inside for each attraction.