I use glass mason jars—specifically, half-pint or pint-sized containers—because glass doesn't absorb oils and doesn't leach chemicals into your spices over time. Fill your jar leaving about a quarter inch of headspace, which allows for minimal air circulation without creating a seal-breaking vacuum. Plastic containers work, but they're not ideal for long-term storage because spice oils can degrade plastic over years.
Labeling is non-negotiable. Use a permanent marker and write "Chai Seasoning Blend" and today's date directly on the lid or on a label affixed to the jar. This seems small, but I promise you, in two months when you're looking at three identical spice jars, you'll be grateful for the clarity.