To unlock different endings, complete the required task during the final mission before the bomb is disarmed.
Complete the special objectives in single player mode to unlock new equipment. (Alphabetical Order)
At the end of this level, when you are supposed to use a sniper rifle to shoot Hamza Hishima, do not kill him. Instead, wait until the crane you are on falls down. Emile will yell at you for missing Hamza. Your character will then turn off his radio and the level will be extended by several minutes.
Reach the required rank to unlock new skins.