All Ammo and Items Code:
Take out the pistols. Take one step back, then one step forward. Squat, and release the button. Turn around three full times. Then do a backflip.

Blow Lara Up:
It is the "explosion" code. To see it, do either the skip level or all weapons cheat, but don't draw your pistols. Lara will die in an explosion that's unforunately a lot less cool than the one in TRII when Lara neglected to draw a flare.

Level Skip:
Take out the pistols. Take one step back, then one step forward. Squat, then release the button. Turn around three full times then jump forward.