Hi Richard!
Welcome to the Thorn Cycles Forum, and best of luck on your upcoming world tour -- a wonderful trip awaits!
A good starting point for recommended Rohloff spares can be found in Andy Blance's publication,
Living with a Rohloff. It can be downloaded here:
http://www.thorncycles.co.uk/thornpdf/ThornLivingWithARohloff.pdf The list appears on page 22.
This guide has been recently revised, the key point being these are the tools Thorn consider absolutely necessary to provide field support for a trip such as yours. If the trip is an extended one, I would suggest carrying a second oil-change kit...not that the distance or time would necessarily require it, but a flush-and-refill seems to cure many of the shifting and smoothness problems that can occur, not matter how unlikely. Flushing out the odd bit of debris or removing wear particles does wonders if the hub does't work well. Rohloff spares aren't commonly available in the back-of-beyond, and carrying spares is less expensive than the cost and delays incurred by shipping.
Rohloff hubs are overwhelmingly trouble-free in most use, but if problems do occur, they seem to have a greater incidence fairly early in their lifespan. Accordingly, I would suggest putting some distance on the hub before your departure. That way, if any problems come to light, you'll still be near home and less inconvenienced.
Others will be along shortly with their own good suggestions, but this should get you started.
Best,
Dan.
