Remark: You are Nerds. So what's wrong with the T-Shirt?:
The other first person action adventure i had these days was an odyssee through the net world browsing for good games. Diggin through all the crap the discoveries and ugly surprises were much less pleasant than in those in BlackPlague.
So, i'd say Frictional deserves some very special kind of merchandise.
The mug is only good, if the coffee tastes and looks like sewage water anyway.
Some kind of Shirt might be nice just showing the infection point on the neck. (though i don't really know much about that yet)
I think the initial text "There are things i need of you. Things you may not understand ..." would be perfect for T-Shirt Print too. Keeps some kind of obscurity.
Then there are the tools: Torch, glowstick, saw, hammer, lighter, crowbar... things that come handy anyway. Nothing that will just get dusty on some shelves. Just make them look and smell like coming directly from the mine.
You could have the inside glowing artifact serving as a hard drive or housing a complete computer while giving your room the shivering dusk at night.
Finally I absolutely want a T-Shirt with Jens' face on it, or an autograph card, at least if he's still looking as cute as on the tiny avatar when the picture is enlarged.:redface: