Lihit Lab is a Japanese stationery and office supply company that's been around since 1938. One of their high-quality products, this book-style pen case, allows you to store and organize all manner of stationery inside.

It features a three-sided zipper opening that allows it to open wide like a book, and has an inner "page" that divides the bag into two sides — one with straps for holding writing utensils (particularly those with clips):

...and another with pouches for holding small items (erasers, sharpeners, small rulers and scissors, lead packs, etc):

Each pen case is $9–$11 on Amazon depending on your color of choice:

• Black ($10)
• Jet Black ($10)
• Brown ($9)
• Blue ($10)
• Coral ($10)
• Yellow Green ($9)
• Orange ($11)