Thanks for posting this here.
The cards inside are most likely “just cards”. The trays inside are used during the game of Bridge Whist. Here is the Wikipedia article on it: https://en.wikipedia.org/wiki/Bridge_whist
I think it’s very neat that you still have the case for them! I’ve seen many of these trays fly by on eBay but never with the holding box with them. So cool!
Hope this helps 🙂