Save health packs:-  You can save health packs by going to a different level, then coming back for health because the levels are so numerous and close together. 

Save explosive ammunition:-  Save explosive ammunition (grenade launcher, Cross Bolt, etc.) for tougher opponents when fighting the skeletons by using the shot gun against them. Get the skeleton between you and a ledge and blast it. The skeleton will fall off the ledge and cease the exist. Since shot gun ammo is more prevalent in the game than the explosive ammunition, this will allow you to save it times when there are no ledges to help.

Unlock All - Have Lara face exactly north and enter the inventory screen. Highlight the "Small Medipack", then press L, Up, X, Up, R, Y. All weapons, unlimited ammunition, and unlimited medipacks will be available. Note: Have her hang from any north-facing object to face in that direction easily. 

Unlimited Laser sight ammunition - Have the crossbow or revolver combined with the Laser-sight. Zoom in, hold L then press Start. While still holding L, select the pistols and press A. While still holding L, exit the pause screen. The sound of the pistols being drawn will be heard. Note: This can be repeated as needed.

Lighting flares - Press L + R when Lara does not have any weapons in her hands to light a flare.

Hint: Turning on all the switches in the Star Room in the Lost Library:
First, start at the switch across from the reset pad. Face the reset pad and number each switch starting with the one you are at as "1" and then going left, 2, 3, 4, up to 7. Then, activate the switches in the following order: 1, 3, 2, 7, 5, 4, 6.

Killing knights - To kill the knights found in The Lost Library, shoot the blue gem in their chest. Do not attack from the back, as it is just a waste of ammunitions. Six or seven direct hits with the shotgun or the crossbow will kill them. 

No damage from Horus - Step into the blue light Horus was standing in before you put the armor on him. He can keep attacking, but it will not get through the light. Do not get behind it. If you do, his weapons will still hurt you. You must be inside the blue light. This works best when the "All weapons" code is enabled. 

Underneath the Sphinx: Getting out - You can sneak past the bulls without waking them or worrying about locking them in their cages. First, make Lara face north and enable the "Unlimited items" code: Open the inventory screen and you should have all four keys you are supposed to collect in the level. Go to the far right and walk slowly past the cage and the pillar. Then, sidestep to the right until you are almost in the right corridor. Then, go behind the bulls and enter the stone tablets: right, left, middle. Sneak to the left and go to the gate you opened. From there, cross the two pits and place the keys in their correct locations. Go through the gate you opened and head across the monkey swing. Grab the scriptures and exit the level by the monkey swing. Remember to walk across the empty room after the scripture room, as there are spike traps located there. 

Chambers Of Tulun - Avoiding damage - In big room in the Chambers Of Tulun where the man that makes shockwaves chases you, wait for a gold beetle to appear then start running around. The beetle will grab you and you will hover around. If you move too much, hit a wall, or get hit by that man, the beetle will let go, slice up your neck, and you will take damage.
Sent in Tony Mason

Cheat mode:-  Have Lara face exactly north and enter the inventory screen. Highlight the "Small Medipack", then press L, Up,
X, Up, R, Y. All weapons, unlimited ammunition, and unlimited medipacks will be available. Note: Have her hang from any north-facing object to face in that direction easily.

Level skip:-  Have Lara face exactly north and enter the inventory screen. Hold L + R and press Y. to advance to the next level. Close the inventory screen to advance to the next level. Note: Have her hang from any north-facing object to face in that direction easily.