A converter for a Lamy fountain pen holds ca. 1 ml ink. Being en route one has to restrict oneself to manage with that amount. I use document ink by De Atramentis. It comes it beautiful glass bottles, which are unsuitable for travels. Unless manufacture takes pity on urban sketcher and produces cartridges with waterproof ink, we have to think of something else to transport it while travelling.
I was mixing my own ink colours for my trip to Antarctica. I also bought one of these travel sets with refillable plastic bottles. I labelled every bottle, closed it carefully and mad a tipping test. Then I put the bottles into a little resalable plastic bag, this bag into a zipper bag and the zipper bag into a rucksack, which I stored into my suitcase. And I did well to do so. Unpacking in Buenos Aires I found this.
The whole ink was leaked – fortunately the mess stayed in the zipper bag.
For the Palladian Odyssey I decanted the ink into little glass bottles. Originally, they contained very helpful stomach drops. The bottles come in two different sizes. They close drip proof and have a little plastic device that allows the liquid to trickle only drop-by-drop.
I use a syringe with a hollow needle (available at the next pharmacy for a few cents) to decant the ink. The needle fits perfectly through this device. Now not a single drop spills while decanting.
As an additional precautionary measure, I put the bottles into resalable plastic bags, which I put into a padded pouch. (I cannot remember where I got mine but I believe bubble wrap will do it, too.) Then the pouch comes into a zipper bag. This sounds much more complicated than it really is.
I strongly not advice to refill a cleaned Lamy cartridge with you own ink. I did this once in the interest of reusability. While being closed the ink leaked into the fountain pen’s cap. It was a bad surprise opening the fountain pen and watching how the ink purred over table and floor. But since then I know that Lamy caps close ink proof.