I'm not sure specifically what the'sama sama letter day story' is about as it's not a widely known common story. It could be a very personal or a story from a specific local or cultural context.
The 'isekai survival meshi novel' might be special because it could bring in elements of both adventure and cuisine. In an isekai setting, the character has to adapt to a new environment for survival. With the focus on'meshi', it may explore different kinds of food from the isekai world, like strange fruits, magical beasts that can be cooked, etc. This combination makes it stand out from other novels in the genre.
I'm not sure specifically as I haven't read it in full. But usually in an isekai novel, there is a protagonist who gets transported to the other world. In this 'isekai survival meshi novel', it could be someone who has a particular interest or skill related to food or survival.
The Dungeon Meshi anime typically ends at a specific point in the manga storyline. However, it might vary depending on the adaptation decisions made by the producers.
The Kaguya-sama manga is indeed finished. It ended after a successful run, leaving fans with memories of an engaging and enjoyable story. The final chapters tied up loose ends and delivered a conclusive ending.