You can carry a pen and many small stationery items in a flat place. It is easy to find the desired pen or accessory because it can be viewed in a two-page spread. It's slim and easy to carry. It fits nicely in the bag. With a pocket on the front.
The Pen Addict
LIHIT LAB. Zipper Pen Case, Multi-Layered Storage Large Wide Open Pockets, Straps and Pouches To Store Stationery - AliExpress
Lihit Lab Pen Case Flat Type - Green – Nero's Notes
At a glance this might look much the same as any other pencil case. It's when you open it up and look inside though, that it starts to make more sense. Unlike any 'normal' pencil case, this one features a nice wide main compartment, with extra organising mesh compartments running along the long edges of the inside of the case. These compartments can be used to keep smaller items together and prevent them from falling to the bottom of the case.
Lihit Lab Wide Open Pen Case Yellow Green A7688-6
JetPens.com - Lihit Lab Smart Fit Double Pen Case - Large - Blue
Sumo Paint 5.0.4 Free - Colaboratory
LIHIT LAB. Zipper Pen Case, Multi-Layered Storage Large Wide Open Pockets, Straps and Pouches To Store Stationery - AliExpress
Sumo Paint 5.0.4 Free - Colaboratory
Lihit Lab Compact Pen Case Navy A7687-11