A few days before the BioShock Infinite release, 2K Games company announced the Season Pass for the game that will include three large DLCs and The Early Bird Special Pack, which is available only to the ticket’s owners.
At the moment, the developers are only planning to release the first expansion pack that is likely will contain a variety of achievements and improvements, both for the characters and for their ammo. In addition, the producer of the project, Ken Levine, said that they are going to:
"...reveal hours of the new gameplay and allow the players to learn more about the city of Columbia and its inhabitants."
Although the BioShock Infinite DLCs will be released not soon, but you can buy a Season Pass only for $19.99 in Steam and receive The Early Bird Special Pack, which includes improvements for the machine gun and the pistol, as well as gold skins for them, 5 bottles for enhancing various parameters and other useful stuff, already now.