To unlock the following items you have to beat the complete game as described

Unlockable	How to Unlock
Alternate Title screen	Beat the game once
Chris' Alternate Costume	Beat the game once as Chris
Chris' costume from Resident Evil: Code Veronica	Beat the game twice as Chris
Hard difficulty	Beat the game once on Normal difficulty
Invisible Enemy Mode	Beat the game thrice on Normal or Hard
Jills Alternate Costume	Beat the game once as Jill
Jills costume from Resident Evil 3: Nemesis	Beat the game twice as Jill
One Dangerous Zombie Enemy	Beat the game as Chris and Jill
Real Survival Mode	Beat the game twice on Normal or Hard
Rocket Launcher	Beat the game on Normal or Hard in under 3 hours
Samurai Edge Handgun	Beat the game on Normal or Hard in under 5 hours