Contrary to popular interpretations, chests brimming with gold and jewels were rather rare during the Golden Age of Piracy. Burying treasures in any form was rarer still. The only documented case concerns William Kidd's attempt to use some of the wealth he buried on Long Island as a bargaining chip to avoid punishment for piracy. That tactic failed miserably for him, he was hanged.
While English fiction helped popularize the myth of buried treasures, pirates were much more practical, looting food, water, alcohol, ammunition, rope, canvas and wood from ships to stay afloat. They sold anything they couldn't use, including looted valuables to pay for the crew and turn any profit from their endeavors... Which was often spent carousing on shore.
There have been ships filled with gold and treasures but they were usually warships under heavy escort. The average pirate ship could not hope to successfully overtake such tempting targets... with a few notorious exceptions. Still, a lot of commodities we consider of little value now were very valuable then because of rarity. Things like spices, fabrics and dyes were common types of pirate plunder.