I did a 11,000 mile tour and changed my chain 5 times which kept my rings and cassette in fine shape. I never had chain jump even after the last chain replacement. I would carry an extra chain when you know you won't be able to get one for 1-2k miles or have someone send one general delivery to post offices along the way. I did this for a friend who cycled in Africa and he always got his parcels but I am sure a lot of that might have been luck. Anyway, replace your chain fairly frequently and the rest will last you. I personally wouldn't carry a spare cassette.

You already have some great advice regarding lubes. A small bottle will last you for quite sometime and when you run out, you can always find something that will work like asking at an automotive garage for whatever spray lube that might have on hand etc...