Unstable Ordinance is an item in the sixth catalog, Shop & Awe. It cost 70 coins and takes a minute and 30 seconds to deliver.
This item is a small grey bombshell. When burned, a red light blinks and beeping could be heard. After a few seconds, the item blows up and smaller versions of the item drops from the sky in a line, blowing up whatever was below.
Still blinking after all these years.
Unstable Ordinance + Ordinary Brick = Brick 'n Mortar COMBO
Unstable Ordinance + Railroad Xing = Planes & Trains COMBO