The soil of the Terran Empire's planets are full of valuable materials.
Large quantities of graphite, carbon, gas, oil, deuterium, hydrogen, antimatter, zero point energy deposits, aluminum, titanium, platinum, diamonds, white phosporus, coal, petroleum, plutonium and uranium give the Empire a stable position on the galactic market.
Because the Empire has and little room for livestock, and lacks major forests, meat, dairy and hardwood are the Empire's main import products.
The Empire trades its services for payments in sodium, potassium, sulfur, granite, meat, wheat and grain, because it's own stocks of these materials are inferior compared to those of its neighbors.
Because of heavy bombing, reshaping and terraforming, even ice planets have become somewhat arid, though the hotter planets have become cooler.
Both international imports and exports are fairly high, though the large, fluctuating internal economy determines the prices.
The Terran currency is the Terran Dollar; one Terran Dollar is worth $US 8,- at the US Dollar's peak.
One would think that, because of Terran technology being able to infinetely copy all resources, trade wouldn't be necessary. Some foreign powers have resources of a better quality than their domestic counterparts, but more importantly: copied resources are more impure and have a lower quality than the original. Thankfully, copies of copies retain the same features so the initial quality decay is also the only instance.