I haven't taken a trip of that length.....yet. Most I've made is a couple of 600 mile trips. From what I've read, the belt should be of no concern. Aside from the standard pre-trip oil change, inspection, etc.; the must haves, in my opinion, are:
Spare fuses. 20amp
1 qt of your favorite oil. The bike's been known to use some on long rides.
A spare container of fuel
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These seem to be favored by the ADV rider group. REI, and Cabella's carries them. I did run out of gas on one of those long trips due to miscalculating headwinds. 20 oz of fuel can make the difference between a long walk and a short refuel to get you going again. It may only weigh short of 400lbs wet; but it really sucks to have to push that load.
Count on rain, no matter the forcast. Count on cold if going to higher elevations. Bring appropriate gear.
Have some water and a snack. DON'T count on making it to your next stop for groceries. If, heaven forbid, you do get stranded; you'll want something to munch on. A bottle of water and a granola bar don't take up much space.
Basic tools. Not the Suzuki crap that comes with the bike. Get some real tools, and practise doing some of the things that might happen on the road
WITH THOSE TOOLS. It sucks to get out in the middle of nowhere, need to take the seat off to get to the spark plug and realize that the wrench that fit in the garage, won't actually budge the bolt on the side of the road.
A spare spark plug.
A flashlight.
Duct tape.
Zip ties.
Electrical tape.
One of those thermal blankets that looks like a big piece of aluminum foil. If you get stranded at night it'll keep you warm. Makes a decent ground cover too.
Controversial; but I do take a can of Fix-a-Flat, as well as a Co2 inflator. If it's just a puncture, you can use the Fix-a-Flat to get it to hold pressure, roll it at low speeds for a couple of miles to get the goo to set, then reinflate the tire with the Co2. Won't work on major blow outs or the like; but it might be the difference between getting you to the next town, and a new tire and tube, and calling for a tow.
Fully charged cell phone. I use a Tracphone for travel. Cheap, not a huge loss if lost or stolen, and I've never had a problem with signal anywhere.
Leatherman type tool.
Throttle Rocker. I have the left and right hand. Your hands will thank you.
A good pocket knife. Not a little "apple peeler", but a good solid folder, with a legal blade.
That's about all I can think of at the moment. Peruse some of the long distance MC travel sites, like ADV rider, for additional tips. Mount up, have fun, and take some pics!
Have a safe trip.