We carry few spares as we travel but do carry wheel bearings, a fan belt and brake pads.
When we drove across Labrador we stopped in one campground and this older man (my age) said to us that his son owned the campground and had gone into town to get a trailer axle. He was building a trailer for his dad in the back yard. I went out to see this.
This was in Labrador City, Labrador/Newfoundland, maybe 7,000 people in Labrador City and greater Labrador City yet you could buy all the stuff to build your own trailer.
It may be that if you're not carrying a spare set of bearings you should at least know what size you need.
We had our first opportunity to use our AAA road side service in Canada this week. I had rotated the tires
and left the key in the ignition after re-pressurizing the rotated tires
. (Labrador City is literally many 100s of miles from any true commercial center though they do have a Walmarts and a Tim Hortons.)
That night as we were heading out to a concert, I couldn't find my keys and remembered that I had left them in the car in the ON state. The battery
was dead so we called Canadian AAA and they appeared within 10 minutes and we were on our way.
We do have temperature sensors on our trailer tires
(and the Honda's rear tires). I'm not sure if enough heat would be conducted from a bearing failure to activate the sensor because it hasn't happened yet. When we stop we always touch our trailer hubs (and Honda hubs). I do know a brake failure will heat up the sensors quickly and be detected by the tire monitoring system.
The more 'out' you get the more likely you are to find self sufficient people who can help you with a problem. Last year out in the middle of 'farm country' Florida we found a welder to fix our broken frame, a great job at a fair price.