The following are all required to obtain 100% completion:

Storyline Missions (48)
Luigi Gortelli
Joey Leone
Toni Cirpriani
Salvatore Leone
Asuka Kasen
Kenji Kasen
Ray Machowski
Donald Love
Asuka Kasen
Ray Machowski
Donald Love
Catalina

Extra Missions (17)
El Burro
Marty Chonks
King Courtney D-Ice

RC Toyz
Mafia Massacre
Diablo Destruction
Casino Calamity
Rumpo Wrecker

Offroad Missions
Patriot Playground
Multistory Mayhem
A Ride In The Park
Gripped

R3 Missions
Taxi Driver (100 Fares)
Paramedic (Level 12 Complete)
Vigilante (20 in each city)
Firefighter (20 in each city)

Import/Export Garage
Portland Island
Shoreside Vale

Police Vehicle Crane
Police Car
Ambulance
Firetruck
Enforcer
Barracks OL
FBI
Rhino

Achievements
Find all 100 Hidden Packages
Complete all 20 Rampages
Complete all 20 Unique Jumps