Kosteyer Grenade Launcher Attachment:
In Dark Valley's lab, on the first floor, you can find a grenade launcher attachment in one of the many lockers.
Open the console and enter g_always_run 1 to have unlimited stamina and run as long as you want. Enter g_always_run 0 to disable the cheat.
Limited Edition passwords:
Run the program "Setup-bp" in your main S.T.A.L.K.E.R. directory. For the first password, input pseudodog to unlock UK and US multiplayer skins and the Pool multiplyer map. For the second password, enter snork to unlock French and German multiplayer skins and the Dark Valley map.
Thanks to Revolution Readers Stempo, Fredmund and Carte!