The Gold Nugget is an item in Pajama Sam in "No Need To Hide When It's Dark Outside".
Sam will need the gold nugget in order to gain access to the park. Sam will find the gold somewhere in the lower mines (the left side when Sam enters the first fork in the lower mines). Sam will then need to use the pickaxe to mine the gold. He accidentally breaks the pickaxe, but luckily he manages to obtain two gold nuggets, one of which he lets King keep.
Sam will then need to give the gold to the Toll Bridge so that he will allow Sam to go across to the park.
Doing this is optional, unless Sam needs to get his flashlight from the mines.