Only ever had one wheel bearing failure, and it was on a roadie after a head-on and a rebuild, without changing bearing so sorta reckoned it had a reason, my slackness.
My maintenance program has the wheel bearings regreased every few months, checked prior to every ride, and changed every couple of years if there is no other signs of wear.
They have a finite lifespan yes, but you can control the unexpected easily.
I’d be more likely to carry a spareset of brake pads myself, and I already carry a 13 kilo backpack…….. 
Not saying you’re wrong Smithy, but it’s like clutch issues for me, never have them, cause i regularly maintain them.