Explosives aren't all that high energy. For example TNT is only 4.6 megajoules/kg compared to gasoline's 46.4 MJ/kg. The thing with an explosive is that it will release all its energy at once.
I've heard that a block of C4 has the same energy as a block of butter, but I can't a reference to that, and the numbers I just looked up say that butter has a much higher energy density.