This Dialog box lets you transfer commodities between the unit and the city. I loaded my caravan with 20 food units, 15 timber units, and 15 iron units. I’m going to bet that it’s enough to emissary just about anyone I come in contact with.  When it comes to worth, as far as neutral units are concerned, 1 timber = 2 food, 1 iron = 3 food, 1 gold = 5 food.  Hit the OK button and notice the change in the Army Information Window. Now close it to get back to the map. We’ve got the commodities loaded.  Now we just got to get them to somebody.