Kalvos has done some analysis, and here is what he finds.

The two tiniest coins are the Dutch dubbletje and the Russian kopek.

Here is a Dutch breadbox with an angled lid.

Inner dimensions are 28 x 33 x 40 cm
Taking into account volume lost due to the angled lid
      Volume is 29,800 cc

1 dubbletje fits in a cubic volume of .11 x 1.5 x 1.5 cm
      Volume is .2475 cc
Therefore, 120,404 dubbletjes fit into the breadbox
There are 10 dubbletjes to the guilder, so the box contains Fl 12,040.40
At today’s exchange rate (January 6, 2001), that is $5208.54
Traveling back in time with that money, we’d find the purchasing power of today’s $5,208.54 was only $428.47 in 1940.

The kopek is actually smaller.
I don’t have a Russian breadbox, but using the Dutch one as if a tourist
1 kopek fits into a cubic volume of .08 x 1.5 x 1.5
      Volume is .1800 cc
Therefore, 165,555 kopeks fit into the breadbox
There were 100 kopeks to the ruble, so the box contains Ru 1655.55
At today’s exchange rate (January 6, 2001), that is $58.73
Traveling back in time with that money, we’d find the purchasing power of $58.73 today was $4.85 in 1940
However, the kopek is obsolete today, so the tiny coins represent, indeed, a very small fortune

Now, where was I?