Three weapons glitch

The Three Weapons glitch is a Halo: CE glitch that allow players to obtain three weapons on the level, Pillar of Autumn.

Walkthrough
When you finish talking to Captain Jacob Keyes, immediately turn around and go to the spot where you would normally receive ammo for your Pistol. If you reach the corner near the bulletin board before you receive a load-point, you have done all you need to do to start the glitch. The Grunts will not spawn, so you do not have to worry about being weaponless. Move on forward, grabbing the Assault Rifle, and kill the enemies in the mess hall. Pick up a second weapon.

Once all the nearby enemies are dead, go back to Captain Keyes. As soon as you're there, turn right back around and head back the way you came. This time, when you pass the load-point, you will receive Pistol ammo, giving you three weapons: an Assault Rifle, a Covenant weapon of your choosing, and a Pistol. This glitch can be very helpful, especially on higher difficulties.

Not only do you get an Assault Rifle, a Pistol and a Covenant weapon, but you can swap any one of them to any other weapon at any time (of course, no duplicate weapons). You can have any three of the following four weapons: Assault Rifle, Pistol, Plasma Pistol, and Plasma Rifle.