So your PCs have won their quest, be it slaying a mighty dragon with a magical weapon of old, beating a crime boss, or vanquishing a mighty wizard or wight, and they have taken possession of the treasure. Chest after chest of gold and silver coins, gold bars, and every kind of jewel and gemstone is theirs for the taking. If they are not careful, they may find that their trouble has only just begun.
What to export or import....
Fabric: wool, linnen, silk...
Wood: raw-material, furniture
Metals: iron, gold, silver, copper...
Wine, beer, mead, spirits...
Animals: horses, sheep, swine, cows...
Coloring-powder (for fabric, ink...)
Raw-material to make fabric: unprocessed wool, linnen, silk...
Glass: Windows, figurines, glasses, raw-material...
Tea (not sure about my spelling here, but I mean the hot drink Englishmen drink instead of coffee!)