Debug Menu:

Press Start to pause the game then hold L2 or R2 and press left, circle, up, down, right, right, left, triangle, up, down. You will hear a noise. Press Start and then press Select to bring up the Debug Menu. Here you can do very COOL things.

Snake's Tuxedo: To play as Solid Snake in a tuxedo, you have to beat the game two times using your old save data to reload new games. On the third game Snake will change into his tuxedo when he is on the elevator.