When you have been shot, and you badly need health walk up to a wall (any) and stand next to it close he will then lean up against it, it may take a few seconds but wait till he gets off, he will have a full recovery.
Kelvin Deamer mode:
Successfully complete the game to unlock free roaming mode. Then, go to the golf cart that you will find in one of the parks. Press Up, Down, Triangle, Down, Triangle, Left, Right, Circle, to be transformed into a character known as Kelvin Deamer.
Skip intermission sequences:
Press R3 to skip some intermission sequences. Note: Not all sequences can be skipped.
Free Roam mode:
Successfully complete all standard missions to unlock the "Free Roam" option.
Double health:
Press Up(2), Left(2), Right(2), Circle(2), Down at the title screen. The sound of a woman groaning will confirm correct code entry.
Armoured car weapon:
Press Up, Down, Left, Right, Square, Triangle, Circle at the title screen. The sound of a woman groaning will confirm correct code entry. Note: The weapon can only be used during missions