Doesn't writing on a blank cart sorta defeat its purpose? Unless, of course, you NEVER want to change what you use in it and, in that case, why didn't you order prefilled? I use Avery removable 1/4" round color coding labels. Mine came in 4 colors and the color tells me the nicotine level, the symbol or number or initials tell me what's in the cart

I use a fine pen and it has more than enough room to mark it so I know immediately what is in it

I've never had one fall off and they remove easily and leave no residue

I use larger labels in the same colors to mark what nicotine level is in what boxes...I use "more than a box" or any clear container to separate the nicotine levels of the prefilled carts. The filling and cleaning supplies, etc have their own box. I keep juices in their own box...the juice caps have the 1/4" round label I mentioned earlier and it's a perfect fit! I have a number on each of them that corresponds to the index I keep of my supplies (an Excel spreadsheet but paper or cards will work just as well) so I know immediately what the bottle contains just by looking at the top

I have waaaay too many supplies, can you tell

I gotta get to vaping NOW
