There are several nice extras on the Grease 2018 blu-ray release. Many of these can also be found on the 2006 Grease DVD release.
These include:
Black and white scenes not used - 10 mins
Remembering Grease (2006) includes interviews with John Travolta and Olivia Newton-John from 1998 - 22 mins
Behind the scenes photos (including Olivia's mud covered legs after the wave hit them during the beach scene!)
Footage from the 1978 TV special Grease Day USA including Olivia's interview with Roger Stigwood.
Grease A Chicago Story from 2018
Alternative ending
The Moves Behind the Music with Pat Birch - 18 mins
Original song to the animated title sequence
Theatrical Trailer
2002 DVD release party and reunion of cast. Olivia and cast perform Hopelessly Devoted To You, You're The One That I Want and Summer Nights - 19 mins
