Speaking of REI, this is what I use to store Potable Aqua tabs for EDC. This small (really small) capsule holds about 15 PA tabs.

Bison Designs Keychain Capsule

These are anodized aluminium. Will iodine have an effect on these capsules?

I use a blue one for PA and a red one for three peces of Spark Lite tinder and a shortened Spark Lite striker. These go on a split ring with a Silva Companion compass, ACR emergency whistle, Schrade SS1 knife, and Princeton Tec Pulsar II. Along with a Zippo lighter, keys, wallet and Benchmade Griptilian, this is my EDC kit.