Items for trade: see supply and demand. How determined? Seem to include
(in rough order of demand/supply:)
Uranium
Copper
Silver
Dye
Coal
Gems
Silk
Gold
Wine
Oil
Spices
Wool
Cloth
Hides
Beads
Salt

From terrain types: possibly these can be traded:
Forest	Glacier	Swamp	Jungle	Ocean	Desert

Buffalo	Pheasan	Game	Ivory
Wheat	Iron	Furs	Des.Oil	Glac.Oil
Peat	Fish	Oasis	Fruit	Whale	

Coal	Gold	Silk	Wine	Gem	Spice