I use an older Northface zipped pouch (no longer made) for my PSK. For me a PSK has to be more extensive and thus takes more room than would fit into any altoids type tin. For my water purifier tabs and 1 qt playtpus water container--I use one of the viewtainers from Home Depot. It offers some protection for the tabs and the container and still fits into the pouch so everything is in one place. The fire making portion of the kit in one of the witz waterproof boxes as I use wetfire tender and don't want that crushed. I like the pouch for several reasons the foremost being that if want to leave my pack for any reason I can carabineer the pouch onto my belt and always have it with me.

http://www.viewtainer.com/

Regarding Lock & Lock boxes they are great and last. I've not used them for a PSK but for almost everything else.