I confess to carrying both a Fibrefix and spare spokes & NBT2 (as Hypercrackers no longer obtainable). NBT 2 only ever used in anger the once, on my first BCM at Kings, where despite a comprehensive selection of tools and spare spokes, there was on that on occasion no other way of removing cassette - on another rider's bike. And this despite fact that I've never broken a spoke on my own 32/36 spoke hand built wheels.
And a spare tyre, because riding companion suffered a catastrophic blow-out on another welsh 600 some years ago. Never deployed since of course !
Spare cables, chainlinks, all sorts of bits as well as a couple of tubes. Beanie, spare gloves, spare socks, buff are always there because I can never be bothered to take them out. Longer rides like the BCM I add a lightweight bivi bag - again only used once, on a BCM, by another rider.
Yes I carry perhaps a couple of kgs more kit than most, but that's not going to make the difference between success or failure. I'm just happier knowing that for about 99% of all mechanicals I have at least one, if not two, solutions at my disposal.