Just stick with normal scheduled maintenance. Don't go spending a ton of money fixing something that isn't broke.
I got 244k miles out of a 1/2 ton GM when I sold it. Had original u joints and cv shafts. I've got 255k on a ford escape and it has the original cv shafts front and rear, but did require 1 u joint and a carrier bearing a few years ago.
Usually you will get a warning before something fails such as abnormal noise or a slipping transmission, but there can just be a sudden catastrophic failure.
I carry the old serpentine belt and maybe a tensioner with a noisy bearing just in case, but don't pack around spare parts, and surely don't replace something when the current something is working correctly.
