About using the item slots

[Urkle]

there should be no file that would affect the working/non-working of the number keys.. the only reported issue I have for number keys not working is caused by non qwerty layouts..

Now, a possibility is that your settings.cfg got corrupted and "lost" the keymapping. Try deleting the setting.cfg file in your ~/.frictionalgames/Penumbra/Overture directory. This will cause the game to generate a fresh one using the default_settings.cfg file located in the game config directory.

Wait you are using a Mac.. that's the Library/Preferences/Frictional Games/Penumbra/Overture directory