What item was found? What type of value does it have? Would it be valuable to anyone or only to certain people?
Does your character recognize its value right away, or discover as he goes along that the neat little thing he discovered could change his life? Does your character try to find who it belongs to, either to return it or to learn more about it, or does she keep it, hiding it away for herself? Was the discovery of this whatever-it-is really just a coincidence?
Ulterior motiveCoincidences can be dangerous things in fiction. I've seen more than one author make this general rule about coincidences in fiction, and you should probably internalize it as I have:
Use a coincidence to get a character into trouble, but not to get a character out of trouble.
Slipping on the deck and falling overboard is okay; slipping on the deck at just the right moment for the assassin's bullet to miss your head is not. Being attacked by a stray dog on the way home from work is okay; being attacked by a stray dog while you're trying to find an excuse to get into the emergency room is not.
With today's writing prompt, let the valuable discovery get your character into trouble.