This type of trip is my pastime. Trans-America Trail = 6,800km dirt across USA and 6,500km highway to/from. Trans-Canada Adventure Trail =15,000 dirt across Canada. Mexico to Arctic Ocean and others.
A good o-ring or x-ring chain like the stock chain on a new KLR should be good for well over 25,00 km.
New steel sprockets = 15,00 to 20,000 km or more.
New clutch and throttle cables = 50,000 km.
brake pads = over 25,000 km for long distance riding.
The Kenda k270 tires on my KLR now are at 16,000 km and FULLY worn out on a trip from the Texas coast of the Gulf of Mexico to Canada, a few thousand km on the Trans-Canada Adventure Train and back to the Gulf.
I use the same oil for the engine, the chain and the air filter. I have 160,000 on the original filter. I put the filter in a plastic bag with a little siphoned gas and squeeze it until clean, squeeze out out the gas and add engine oil and reinstall with no wait time needed before riding.
I oil the chain each morning or 600 km with engine oil kept in a small medicine bottle and a tooth brush. I do this with the engine turning the wheel. Nothing but an old tooth brush is at risk.
Small 1/4" drive ratchet wrench with 8, 10, 12, 14, 17mm sockets and a short extension. Also, A short piece of pvc pipe with tire irons inside for a cheater lever.
A 10mm wrench for the shift lever pinch bolt and a small adjustable wrench.
Flat blade and Philips screwdriver
The two stamped axle nut wrenches and the spark plug sock from the stock kit.
The two hex keys from the stock kit.
Tube patch kit, a 12 volt air pump and tire irons.
Front and rear inner tube not just the front.
Head light bulb packed with cotton in a medicine bottle.
Chain master link if used.
Fuses. Consider a circuit breaker.
Brake and clutch lever.
Not necessary with new cables but spares strung in place may give peace of mind.
500ml engine oil in a hard plastic unbreakable graduated water bottle.
JB Weld epoxy
Waterproofed wiring diagram
Short length of 14 gauge wire and some wire nuts
Consider checking valve clearances on the new bike and taking one size smaller shims.