Cheat mode:

Press X + B + C at the options menu that appears before game play 
begins The phrase "Cheat mode on" will appear at the bottom of the 
screen to confirm correct code entry. Selectable objects and 
locations such as entrances, enemies, food, etc. will be highlighted 
on the map. Trepliev may be moved instantly from one location to the 
next while on the map screen. All items, weapons, and clothing will 
be available, with unlimited ammunition for the more powerful 
weapons. 

To play the game without the full set of cheats, begin and save a 
new game with cheat mode disabled. Restart the game by using the 
cyanide capsule. Enable cheat mode and load the previously saved 
game. This will enable the teleportation and marked map options 
but keep the items originally present in their normal numbers.

Faster conversations:

Press P to speed up the rate of the FMV conversations.