I've just returned from several months touring in South + Central America. Tyres for 27.5" and 29er were the most common, and generally easy to find in cities or larger towns. I was running 700c and had difficulty finding decent tyres for this size (coudnt use 29er due to clearance issues).
Spare rims/hubs for anything upto 32h are also readily availible, however, as I found out in Mexico, spares for 36h wheels (rim/hub) are very hard to find, and only availible in major cities.
I was running 10 speed, gf running 9 speed - parts for these drive trains were generally easy to get hold of. I cannot comment on availibility of 11 speed components. I would recomend taking a set of friction bar end shifters for emergency use of you break a gear shifter.
Definitly take some spare brake pads - these were very expensive (often 3 times the price in the UK). Given they weigh very little, its worth taking some just for the cost savings, and they can also be hard to find outside of cities (depending on which ones you need).
I was using inner tubes, with several spare tubes on hand, and lots of patches! I would usually get a puncture every 300-500 miles on average, although some days would see multiple flats. I was glad I didnt go tubeless though, as my tyres picked up numerous cuts that definitly would not seal with sealant. I also met other cyclist who were having issues with tubeless set ups and finding hard to find replacement sealant. If you do go tubeless I would take at least 2 or 3 spare tubes for back up.
Make sure you know how to fix your bike before you head out, you need to be fairly self sufficient with bike maintenence. For anyone from Europe, its hard to comprehend how remote some of these places are. For example in Alaska and Canada, we regularly cycled several hundred miles between bike shops (on the Alcan), and there was no bus service or anything along this stretch. Similarly for parts of Patagonia and Northern Argenina - we cycled several days between bike shops or larger towns.
Finally, if you do pickup a serious mechanical, most people drive pick-up trucks and its usally possible to hitch a ride to the next town. Hitchhiking seems extreamely common in Argentina and Chile!