I’ve used the same pencil case for about 5 years now—a small, zippered canvas bag made by Faber-Castell:
It holds more than I need at any one time to work, but having some extra space allows me to bring along more choices. It’s very durable too, having held up under the stresses and strains of traveling through more then a dozen European countries, and as many (if not more) states and provinces across North America.
There are countless products available today (including homemade solutions to choose from) but they all need to provide the same basic functions: to keep things together and to keep things from breaking. But with a soft bag pencil points are vulnerable, so my costlier and harder-to-replace items get added protection in the form of a metal spitzenschoner:
This vintage pencil case from A.W. Faber called Scholars Favorite (no apostrophe) solves the protection problem by being made of wood. The center is hollowed-out and the cap stays on by way of friction (rather than being threaded, etc.).
It has a rather thin diameter so three pencils is about all you can fit inside, but I like this because it seems more purpose-built that way—bring only what you need, plus a spare perhaps. There is another explanation regarding its storage capacity though, having to do with its age:
The original owner of this pencil case had inside it a dip-pen holder as well as several slate pencils (which have a much smaller diameter than graphite pencils), so it could carry more of then-contemporary writing tools. I haven’t seen this particular case in any advertisements or catalogs yet but I’d place it from the 1920s or ’30s. Owing to the use of English on the label, I’m presuming it came from the American branch of A.W. Faber:
One final touch: there is some padding at the bottom on the inside to soften the impact for nibs and pencil points.