@Gray Area beat me to it. I was going to make my own custom silicone cap (3d printed mold, of course).
But
@SSVUN~YAH found these awesome headphone cases, and it's worked perfectly.
I can transport my cap + WPA without any problems. There's also space for a reducer in the case
I took a gamble (colors are random), and got a red one.
For the price, it's build quality is obviously on the lower side. The shell is cardboard covered in fabric But it's small enough to toss in your pocket and know that your cap is safe and sound. I suggest you buy 2-3 if you're going to use them excessively.