Halo: Combat Evolved Cheats

Towards the beginning of the game, there is a way to bypass the two weapon limit and carry three weapons at once. On the first level, make your way to the bridge. After speaking with the captain, quickly run out of the bridge before the chapter name disappears. If you were fast enough, the checkpoint at the door will not trigger. Now run to the mess hall and get your Assault Rifle and another weapon. Now, run back to the bridge and trigger the checkpoint. When you go back towards the mess hall, the pistol will appear in your hands, and you will be carrying three weapons instead of two. Each gun reloads and exchanges normally. Note: This only lasts for the first level.

Simply beat the game on legendary to unlock an additional scene at the end cinema.