I use fabric markers and 3x5" muslin bags. This allows me to name the juice and manufacturer as well as note if the bag is "used" carts or "filled" carts. I also have bags for caps, plugs, blank carts, etc., etc.
My syringes also go in a bag so I use only a particular juice with a syringe. My Volcano supplies are in orange fabric markers and v2's in blue. Everything goes inside one box.
I was lucky that I started this way because I can see how quickly it could have gotten mixed up. I happened to have had a few hundred of these bags (I used to print on them and sell them online as wedding favor bags). Anyway, you can google San Francisco Herbs and search for muslin bags. Buy the fabric markers at Michaels.
These don't rub off if the liquid drops on it like plastic would.