This might not be an earth-shattering tip but hopefully it'll be of service. It was to me.
When I first got interested in magic back in the early 90s, I saw a lot of the guys in the magic store who brought in their cups/balls in a cloth bag with a drawstring. This seemed to be the most common method for carrying the cups.
I ordered some copper Charlie Miller cups from Magic, Inc. and I had the option to buy a leather, felt-lined case. When it showed up, I was so pleased -- it was much more secure than a bag and they didn't rattle around. You just dropped the balls in, stacked the cups up and closed the top.
Anyway, long story short, I was working at a newspaper at the time and had the cups with me at work one day. A guy came by and said, "I didn't know you were into photography." I said, "I'm not." He said, "Oh. Whose lens is this?"
Turns out, that the case that I'd received from Magic, Inc. was a professional lens case used by photographers. And it's perfect. The one I have is embossed on top with "127mm F4.7" which I'm sure means something to those familiar with camera lenses. :) I just know it's the perfect size for the Miller cups....and that apparently many such lens cases are made in a variety of sizes. So, no matter what cups you use, you can probably find a leather, felt-lined lens case that will work for you.
Anyway, I'm a long-time lurker and recently decided to start participating. So, I hope my contribution is of service to someone. Thank you for all you contributions that have served me. :)