A question for the historians of imgur

I'm a high school history teacher who just inherited some neat stuff (through my grandfather) from my great grandfather's time in the US Army during World War I. I'd love to make use of a few of the artifacts in a lesson, but I want to be sure of what everything is first.

My question is what is this metal thing. I'm under the impression that it is some sort of souvenir tin for holding a matchbook or something.

The words on the front appear to spell "Deutsches Eck Coblenz", which I'm assuming means "German something something"(Google translate was of little help)

Side view

The back which looks to be pressed with a map of the Rhine River.

Any insight would be greatly appreciated; thanks a bunch!

As a bonus, here is some more of my great grandfather Ardelt's personal effects