What is it?

[MP38]

Here's another one! Got this case, and I'm not sure exactly what it's for? Has German placards inside, and also has a US Army hand baggage tag, but I can't make out the writing since it's faded.
The only thing I can read is the rank, which says "Capt". There are two doors with storage in it. The top door has a holster in there with room for 4 spare bulbs (only two are left). Top of case is marked "Rkr. 31". if you can read German, you can translate the placards inside, and we can probably find out what it's for just by that? Any help would be appreciated!
Also, any idea of what it's worth?

Thanks,
Matt 8)