Recently there was long thread about the BCA. I can now post possible answers to some of the questions, such as "Why is the BCA still raising membership prices when there is a significant amount still left in its coffers?"
I always carry a spare light (only a maglite, admittedly) but never SRT kit. The way I see it, I never cave alone so, if I did somehow lose a bit of kit I could just borrow off someone else.
Sometines a Patzl Shunt (in case of muddy ropes - would use this as top jammer in that case) otherwise, as others have said, would get by by borrowing other people's stuff.
I just have a little bag with all the emergency essentials - mars bar, survival bag, prussik loop and a pear shape krab. I reckon that should cover pretty much most things. And I really couldn't be arsed lugging another srt kit about- one weighs enough!
I can't see the need, you can just improvise every essential piece of kit. Admitidly, it's not all that efficient but you can get yourself out of a scrape if something fails and you can't borrow.
I always carry a Pro Traxion - it doubles up as a jammer and I find it very useful for tackle hauling - I also have a couple of extra HMS krabs which are good for clipping tackle bags onto my battery belt and again might just see you out of a pickle....