Okay, I’m stumped.
I’ve found three of the fake coins; the tag, the game piece, and the mood ring. Where is the fourth?
And help (even a tiny hint) would be appreciated; I’ve been poking through this game for two weeks and I’m about at wit’s end!
Is it just that nobody has played it, or is it that nobody knows? It’s a pretty enjoyable game, if ridiculously hard for 2009.
I started it after this post! It seems cool, but I’ve barely begun and it also looks hard.
Is it possible to get into an unwinnable state, do you know?
So, I had to peek at the source to figure out which item I was missing. In case anyone gets stuck in the same place I did – the solution doesn’t seem at all obvious to me.
You have to give the sunglasses to the professor.
It’s pretty neat to google the item and solution and see that it’s a real process I just wasn’t aware of. It’s educational IF! 
As near as I can tell, the game won’t let you do anything to make it unwinnable. It’s a fun game, very old school without most of the pain. I was surprised there were no marks for it on the IFDB. I did find the text a little dense at first for a college hijinks game but it grew on me. Very enjoyable!
Edit, okay, I checked and there’s one point where I think it can become unwinnable (but you’d have to solve the hardest puzzle before solving one of the easiest).
General:
Do everything you need to with Neil and Sara before giving anything to the professor in the Physics lab.
Specific: Recruit Neil and wait for the game piece to fall to the ground first.