I use a Nock.co Tallulah as my pen carry case these days. In some periods like now, I like to carry a minimal amount of tools, and it is perfect for that.
I have a brass ruler from Travelers Company, a gel ink pen and one fountain pen in it.
The gel ink pen changes based on whatever I use at the moment. Preferably a Signo DX or Hi Tec-C. But sometimes something else I had laying around that I wanted to use up.
And the fountain pen changes every night / morning after I have filled out my Theme System Journal.
The brass ruler is something I use to divide pages of my A5 Hobonichi Cousin into three to make it fit more tasks.
The gel ink pen usually go in and out all the time. I use the same pen as my pocket pen when needed. And the fountain pen is usually what I use most of them time when I’m at a desk.