I have been using the small Altoids tin. Can put 4 carts in it, plus I also have a spare atty taped to the inside of the lid incase the one in my eRoll happens to die on me while I am out and about.
This is how I carry my eRoll tanks and atty:
Four tanks total in a small Altoids can, the atty is stuffed inside the rubber share tip (for friends). And if you arrange it the exact way as shown, there is absolutely no rattling. The 3 horizontal tanks will press down on the rubber tip, providing a very tight fit. Easy to get the tanks out too.
What do you use as a share tip for the eRoll?
I bought this one to carry my cartridges. I'ts waterproof. Waterproof Medicine Bottle for Outdoor HUI-143763 - TinyDeal