Service the bike before you start the trip, and then have a shakedown ride for anything that the service might have missed or put back wrong.
Bring the tools and spares for expected wear, mostly chain wear (so spanners to loosen the axle and adjust the adjustment bolts) - the standard toolkit has basically all you need but you might want to upgrade some of the tools for better quality.
Bring the tools and spares for some some simple emergency repairs, mostly a tire plug kit & pump/compressor, plus zip ties, duct tape and such.
Bring a first-aid kit for yourself
Bring a cellphone, a credit card and a roadside assistance membership for all other emergencies
Do NOT bring tools to fix things for which you have no spares with you, do not bring spares for which you have no tools with you.
Travel light, travel far.