Keith Hoodlet 
cathos@securingdev i use film canisters, or sometimes just toss cartridges in a side pouch of my pen pouch. If I need to take bulk ink, I use little screw-top 5mL vials (like what goulet uses to package ink samples)
@securingdev for rollerball cartridges, I sometimes grab rubber syringe caps or little scraps of tubing and wedge them over the tip.
@cathos thankfully Zebra ships the replacement ink cartridges with little plastic nibs over the rollerball that break off when you start using them.