Actually Japan did hoard resources. As deathscompanion1 wrote Japan lacked the hard currency to create a really large stockpile but there was some. Ellis in his book of charts 'Brute Force' has some statistics for what Japan did sandbag. Short summary is there was a six to twelve month supply of items like refined and unrefined aluminum, steel, coal, alloys, a few critical chemicals, some rice, and of course petroleum fuels. The stockpiling is a bit distorted in that part of it was not in japan but in Korea, Manchuria, Formosa, & the naval bases on the mandate islands or in newly acquired Indo China. It was not necessary or practical to pile everything up in warehouses on Honshu or Kyushu.
The one critical resource Japan could not hoard was cargo shipping. Prewar about 11 to 12 millions tons capacity were required to sustain japans industry & support military operations in China. Almost half that was in foreign flagged ships. When the embargos went into effect in mid 1941 Japan was left with about six million tons in its control. So, Japan started the war nearly 50% short of cargo ships just to keep its factories operating. That was further aggravated by the need for civilian cargo ships to support military operations across the Pacific. In 1942 a bit over one millions tons of captured and newly built capacity was added. Unfortunatly the gross needed to be doubled to twelve to fourteen million tons to carry everything necessary. Perhaps four million tons were added in 1942-44.