Costume and weapon bonuses:
Complete all of the Snake Tales twice. Complete 100% of all VR missions. Then, complete the entire game under any difficulty setting. Start a new game with the save file that was completed. You should now have access to Snake's Tuxedo and Metal Gear Solid costumes in the items list. The M4 and AK7 rifle will also be placed somewhere within the Tanker.

European Extreme difficulty:
Successfully complete the game under the normal difficulty setting.

Boss survival mode
Successfully complete Sons Of Liberty under any difficulty setting.

Photograph mode:
Successfully complete bomb disposal mode, hold up mode (alternative missions), and eliminate mode to unlock photograph mode in the VR Missions.

Casting theater option:
Successfully complete Sons Of Liberty under any difficulty setting.

Ninja Raiden:
Successfully complete 50% of the VR missions as Raiden to unlock Ninja Raiden in the VR Missions.

Raiden X:
Successfully complete 100% of the VR missions as Raiden and Ninja Raiden.

Pliskin:
Successfully complete 50% of the VR missions as Snake.

Tuxedo Snake:
Successfully complete 100% of the VR missions as Pliskin.

Metal Gear Solid 1 Snake:
Successfully complete 100% of the VR missions as Snake, Pliskin, Tuxedo Snake, Raiden, Ninja Raiden, and Raiden X.

Alternate ending sequence:
Successfully complete a Snake Tale to unlock the M9. Begin game play and use M9 to stun the Bosses instead of killing them to view an alternate ending sequence.

Easier Pull-ups:
Instead of doing half an hour of pull-ups, go to a place with two rails at the top and bottom, evenly lined up. Then, do the hang-drop-catch ten or twenty times to get a fast level 2 and 3 grip.

All VR missions and characters:
Start a new Missions file, then enter UUDDLRLRBA as a name.

Digital camera
Successfully complete the game. The digital camera will be available when a new game is started.

Guard with red eyes:
Whenever you kill a guard and shoot his eyes, they normally will not get bloody. However, there is a guard in the Plant chapter where this does not happen. After you have defeated the Harrier you will proceed to a path on the side of one Shell. You should find a guard on the roof that urinates off of it. Use your silenced AK to shoot him down. This is very difficult, but you can have a chance to shoot his head when he speaks about his urge to urinate. If you miss the first time, shoot the wall under him. He will walk to the noise, then return and begin talking again, giving you another chance. When he falls, approach his corpse and shoot his eyes, which still will be open. They will have blood in them.

Rubber duck:
You can find a rubber duck in the water floating in the basement of Shell 2 Core (under the hard difficulty setting). On the way to find Emma, at the second air pocket just before the hallway with two mines, there will be a little yellow rubber duck floating.

Sunglasses:
After completing the game two times, Snake and Raiden will be wearing sunglasses.