Why bother carrying it, then? My philosophy is to minimize carrying redundant (radio) equipment [notwithstanding the spare pencil]. I refined my ‘pack list’ over years to minimize weight, setup/pull-down times and faffing about [BTW: I’m not talking about safely items like bothy bags and extra winter clothing]
If I were travelling a long way to the activation (especially an overseas one) I might have a bit more redundancy and definitely do a dummy-run set up/on-air test at home to ensure I’d forgotten nothing and everything works.
As I often want to do 2m FM (for local/regional chasers) and my KX2 doesn’t have VHF, I often take my 2m FM HT as well - that’s a bit of unintended redundancy. I know a couple of summits which are 2m FM dead zones so occasionally that pays off.
But I’m phlegmatic about the very occasional ‘failed’ activation - I (and my dogs) will have enjoyed the walking and it’s an excuse to revisit the summit another day.