Coffee!

[Mister Underhill]

The risks in trading in those lands were rather high for the dwarves, but the coffee trade, cheap and plentiful in the Far East and South, expensive and rare in Middle Earth, was exceptionally profitable. It was relatively light, travelled easily. Passed as ordinary beans to the ignorant, thus avoiding all kinds of taxes, tarrifs and thievery. More than one dwarf expedition, robbed of their gold by bandits, came through with their coffee profits intact. So no dwarf caravan from the east failed to include this "insurance policy."

I smell RPG (and the aroma of slowly roasting Far Harad beans).

Your speculations could also provide the basis for a new theory regarding the Paths of the Dead. The Oathbreakers: restless spirits or deprived coffee drinkers?