DLC pre-included aren't new missions but extra weapons and that sort of stuff.
For ex - The Early Bird Special Pack contains four pieces of gear, a machine gun upgrade, a pistol upgrade, special skins for both weapons and five Infusion bottles (or phials) to increase your stats.
The Early Bird specials are activated upon entering the Blue Ribbon Restaurant area of the game. Here, your weapon skins will be activated, you will find the 4 pieces of Gear on a table and the 5 Infusion can be found on the bar and another table.
See - http://www.ign.com/wikis/bioshock-infinite/Early_Bird_Special_Pack