Here a nice little list from the IGN Wiki that confirmed stuff for GTA Online. There is this and more...
Create a customized character
Develop a backstory for your character
Backstory determines starting location
Join a crew
Rob a convenience store with a friend
Customize a mask for GTA Online
Yell into a controller microphone to make a hold up go faster
Freely divide up money after a heist
A mission called Titan Steal has you stealing the Titan cargo plane
Fly with your friends in an airplane
Race anyone, anywhere, anytime by dropping a marker
Play multiplayer Golf or Tennis
Play a 4-player Golf game
Purchase a safehouse
Watch TV with your friends
Watch Weasel News helicopter footage of your friends doing things
Smoke pot with your friends in your safehouse
Shower to wash off blood
Use an ATM to deposit money
Steal your friends' undeposited money
Play a "deathmatch" game
Design a "deathmatch" game
Go to a Strip Club
Watch a movie and comment on it as a group with friends
Vote on mission playlists
Play 500 pre-made missions, more will be added