All Shop Items
Go to the factions screen in your PDA (subscreen) and enter this code DOWN, DOWN, DOWN, DOWN, UP, LEFT, RIGHT, RIGHT on your D-pad.

Skins for National Treasures
You will have the cheat instructions e-mailed to your PDA when you meet the requirements.
20: Indiana Jones (PS2)
30: Play as civilian doctor
40: Play as civilian prisoner
50: Play as Ace of Diamonds
110: Play as SKU Elite Soldier

Skins for Blueprints
Note: You will have the cheat instructions e-mailed to your PDA when you meet the requirements.
20: Play as Mafia Heavy Soldier
30: Play as NK Elite Soldier
50: Play as NK Numeric Card (Spades)
110: Play as Han Solo (PS2)

Invulnerability
Note: Saving your game with this cheat on may result in it being on permanently.
On the PDA's faction screen, enter UP, DOWN, UP, DOWN, LEFT, RIGHT, LEFT, RIGHT on the D-Pad. You should hear a click that signifies the code is active. The merc will be invulnerable to all sources of damage (you may have to Medivac if you fall into deep water). This also applies to the current vehicle the merc happens to be operating at the time.

Add $1,000,000
Go to the PDA's faction status screen and enter the following on the D-pad: RIGHT, DOWN, LEFT, UP, UP, LEFT, DOWN, RIGHT. A soft click should confirm the code's activation.