I did a tour, they mentioned how a bunch of the low end labour used to wear "ugg" boots which are ankle boots made of sheepskins, wool-side inside. They made great stow-away for a few $2 coins from time to time, no clinking because of the wool. But if you got too greedy the boots started to sag...
I suspect it's apocryphal. Ugg boots sag anyways.
To the high-tech machines: the CSIRO (national science and technology research and tech commercialisation body) did work on high energy beam deposits, to make the die surfaces last longer. They were on the brink of exploring holographic coin prints when I went round, having just done bimetallic inserts and colour. At the rate of stamping, you loose the fine detail on the queen's face very quickly. The trial of the pyx is about this kind of qualitative judgement: Is this coin manufacture good enough to be kept as a mint?
At least one escape caper film (French?) has them use the aluminium coins as welding rod, making a digging tool to get out of the cell (using 200v sparks from bare wires to weld bits of metal together) -francs outre-mer I saw in Noumea were aluminium, featherweight coins.
The 1 yen coin is so light it will float on water.
The jokes about the cost of making a coin exceeding its face value (Pratchett) have some validity. Coins are solid expressions of value but their utility is their movement more than their actual denomination. Hence currency..