I think the best way to answer you would be to show some examples of treasure rooms:
First decoration made by Monzcarro Murcatto:
As you can see, it used stacks of gold-colored items, such as:
Pirate Coin
Ground Reed
Scarab Coin
Gold Ingots
Gold Token
Small Treasure Chest
Gemmed Lamp
Emerald Bangle
Gold Nuggets
Jewel Case
In addition, many gold-colored amulets, pendants, and other accessories were used, often at the top of each stack to add nuanced accents to each SQM.
Another decoration I wanted to mention is the one made by Norelli. Here, a similar scheme was used.
Ewer, which you can take from Razachai Palace, can also be a very good addition.
Some other items that will work well with the treasure room theme:
Golden Sun Coin
Bar of Gold
Gold Nuggets
Next decorations that may help you get some inspiration are the ones made by Norelli and me:
Finally, another great example was made by Mythmine:
In all three decorations, you will find elements related to pirates and pirate treasure. Although we used Incomprehensible Riches from TibiaStore there is quite a significant amount, using the previous suggestions you can swap these stacks for Pirate Coins and achieve a very similar and equally attractive result. What's more, based on these decorations, you can name some more items that can perfectly reflect the vibe you mentioned.
Model Ship
Old Map, Treasure Map, Map
Galthen's Satchel
Compass
Hook, Eye Patch, Peg Leg, Pirate Hat, Pirate Knee Breeches, Pirate Shirt, Pirate Boots, Pirate Tapestry, Pirate Bag, Pirate Backpack, Pirate Voodoo Doll, Ron the Ripper's Sabre (or normal Sabre)
Try to use telescopes, to emphasize the explorer's style.
Bejeweled Ship's Telescope
Telescope