Anyone know what an unopened Coogan's tin should look like?
 

Picked this up today at an antiques shop... can't open it, and it definitely sounds like there is some broken up wafers floating around. Thoughts? Should I crack it?

That is about the right size/shape for a Colgan's Chips tin. I don't think Jackie Coogan ever made any. Nor do I think they're post-war.
Good luck if you decide to open it. Does it say Colgan's chips on the front of the tin? Is it sealed and would show that it's been opened? Or do you think this may be an unopened one?

I would definitely try to open it - just to see if the card that came in it is still inside.

If you don't want to damage the tin, maybe you could try to steam it open somehow, or use one of those jar lid gripper pads (like one would use on a brand-new jar of pickles). If it's rusted closed, you could also try a couple of drops of Marvel Mystery Oil or Kroil to penetrate the space between the case and lid and loosen the bond.

Good luck - and be sure to let us know if you are able to get it open!