The Anasazi or ancestral Pueblo people of the American southwest drank a lot of chocolate. According to a new study, cacao residues detected on pottery show that both rich and poor Anasazi people drank chocolate. One thing they traded for it was turquoise, since sourcing studies have shown that some of the turquoise found at Aztec and Maya sites came from the American southwest. Note that they drank their chocolate unsweetened, a bitter brew like black coffee.
This exchange raises the question of what it is that people want badly enough to trade for it over long, dangerous distances even when it has to be carried on somebody's back. The main answers seem to be jewelry and mind-altering substances, perhaps especially rather mild mind-altering substances like wine and coffee.