On the chain and sprockets:
1. Always replace them together - a new chain on old sprockets will be an old chain after 100 miles.

2. I would say a chain should get to the 10-15k miles range with all the provisos markharf says.

3. I'll also venture out and make a highly religious statement. Stay away from the god awful abomination that is the Scottoiler. It is simply impossible to keep one correctly adjusted on a trip with 20C temperature swings each day, and you're forever skirting the pain of an unoiled chain wearing and an oil covered rear wheel.

4. In another highly religious statement, focus on cleaning your chain rather than oiling it. A wipe with a kerosene dampened cloth each day will do way more to prolong its life than oiling. Some people use WD40 to oil and it sounds like their chain lasts just as long. Others will go haywire just reading this. You take your pick, but like I say, focus more on the cleaning than the oiling if you want to extend chain life.

5. On brake pads - hard to say, but even with very heavy usage 10k miles should be expected. I'm on 9k miles on my EBCs and they have plenty of life in them, though that is mostly with all day cruising on asphalt with little break use.

On brake pads and sprockets
 

Hi,

On brake pads - Sorry to disagree with previous poster, but my experience is that on dirt or gravel roads, brake pads wear down very much quicker, especially if as you say you are hard on the brakes. I would not bank on more that 4000 miles, and would always have a spare set for front and back with me. There is also the sintered pad material vs organic pad material decision. Sintered last longer but ware the disc out more quickly (but not likely to cause the disc to be replaced during your trip, I guess).Many prefer the feel of sintered too.

On sprockets - I would consider just carrying a spare front sprocket, and a few tab washers for its nut, if it uses that system. Assuming that your chain size isn't unusual, obtaining a replacement chain shouldn't be too difficult. Chances are the rear sprocket will fit a few makes and models and you stand a chance of finding that too.(worth doing a bit of research on this though). And if it is flat, as a last resort you can just turn it over as most of the ware will be on the driven side of the teeth. The front sprocket probably doesn't fit any other makes, making the chances of finding something from another bike that fits much less likley. And being much smaller than the rear wears down a lot more than it, and often has a shoulder that prevents them from being turned over anyway, so I carry a spare one. Plus its quite small.

Hope this helps.

Mark