At pause screen press Select, Select, Circle, Circle to get cheat mode.

Then enter these codes to activate the following:

Full health
Triangle, Select

All weapons & 50 medkits
L1, L1, R1, R1

Beat current mission
Select, Circle

Ethereal mode
Triangle, Triangle, Triangle, Triangle

View all FMV sequences
L1, L1, L1, L1, L1, L1, L1.

Glitch
Select, Select, Circle, Circle.