>>805400KLR?
Go through the motor and chassis. Two reasons:
One, so you know it's fresh, no outstanding issues. (Bad bearings, gummed up valves, etc). Personally i'd do a new piston and have the cylinder replated while I'm in there.
Two, so you're intimately familiar with the inner workings of it and can diagnose/repair problems when they happen.
I'd do new chain/sprockets, wheel bearings/seals, front/rear tubes before you leave. Those should last the duration of the trip.
Buy spare cables/lines (clutch mostly, but you can do it with brakes/throttle too) and zip-tie them next to the existing ones. If you lose a clutch cable, you don't have to disassemble/reassemble, you just disconnect the old one and connect the replacement that's right there. Obviously tape off the ends of the new ones so they don't get shit in 'em.
Bring a spare tube (a front tube will fit in the rear enough to get you outtawoods), short length of chain with a couple extra master links, spark plug+tool, any other parts you find need replacing in a season.
You'll probably need a new set of tires through that trip, especially if you're offroad. Plan for that accordingly.
Wear your fucking gear. Don't push yourself too hard, that's when bad decisions happen and shit goes south.
>I fucking hate fork maintenance. 
