Penny bunger was a big firecracker, I was only three when oz went to decimal currency but any big cracker was still called a "penny bunger".
As a medium kid, a handful of ramset cartridges in the campfire woke a few people up.
Well as a big kid I spose I can add the odd thunderflash in the portaloo, that always gets a laugh, (as long as you weren't the one sitting on the honey bucket at the time!)
Dad told me a story once where for a while they tried to blow up a brick letter box. They taped 6 penny bungers together, threw it in the letterbox and lit it.
Didn't blow it up but gave it a decent inch wide crack through the brickwork.