This idea came from a friend of mine and I thought it was worthy of a post, so here it is. The idea is that you can cause an explosion using a chemical reaction instead of a simple explosive barrel. Basically, you would have a menu of different chemicals in the Entities tab, such as Alkali Metals and water, spawn the water entity and it is a standard oil drum, spawn Caesium and it is a different colored oil drum - however if you touch these two barrels together, they will react in an incindiery explosion - an explosion from Alkali Metals could also be reached if a barrel of the substance is dropped in water. Other various materials could be included - such as a barrel of Aluminum and a barrel of IronOxide, when touched, they create Thermite. Other, more shock-sensitive compounds could be added - I do not know of any, but I know they exist.
There could also be a timer on the chemical reaction, so that if you launched a missile, a barrel of water would slide down to the Caesium barrel - but would set there for around 5 seconds until the reaction started and the barrels exploded, triggering the internal explosives inside the missile.
I thought it was a good idea, and thought it would be useful for rocket building and bomb making. If anyone has other ideas for reactions or modifications to it, feel free to post any.