Return Stacked Blocks to Inventory
It's possible in the game to stack multiple blocks in a single space. This is often convenient for storage, but when you start running out of block space in a region it can be a pain.
Example: I'm building a big pyramid with lots of layers. Using z-axis lock I know I've accidentally stacked a bunch of blocks on each other while building it. I'm now getting the 'too many blocks in this region' error, and would like to go out and remove all those stacked blocks, but the only way to do this currently would be to dismantle the pyramid block by block to find them.
I suggest a command like /returnstacks which would return any stacked blocks (all but one - so that it doesn't leave a blank space) to your inventory.