Here in the southwest the wax would melt and make a mess. I think Mr. Ritter covered this in his re of a survival kit. Over the holidays I bought some nice tins with small kids puzzles in them. A bit larger than an altoids but much tougher. The puzzles were 50 pieces and reated for 5 and up. Only took me an hour to put Spongebob together. A trick I use is to wrap clear cellophane tape arond the rim of the container, this mad=kes the lid fit tightly, then I use electrical tape.

I came across another possible path to solve this issue. Besides the hard sided bar of soap container, a container for a deck of cards is also pretty close.

An Altoids tin is 4"x2.5"x0.75"

A standard deck of poker size playing cards is 3.5"x2.5"x approx 0.75"

There are some brands of playing cards that are sold in an unhinged tin. Just have to look around for them.

I've gone to Michael's Craft stores and found empty tin containers in various sizes. Also have looked at tin gift card holders from Depot, Lowes, various places. These might do as well.