I had a full inventory, with lots of gems. I did /cnd all, and they turned into leather boots and came out of my inventory. I got all the gems from hunting shipwrecks.
A bunch of various mob drops, mostly leather/foods/feathers and random clutter gem wise I'm guessing, but: 12 Emeralds 20 Diamonds 20 Lapis 80 Iron Ingots 70 Gold Ingots 100 Coal
they dropped on the floor and turned into leather boots, which I didn't have did you have a full inventory? every spot was taken, and then I /cnd'd and instead of the blocks turning into blocks, they turned into leather boots.
