I always carry one, as do my guides. And a length of outer. I’ve had to use it twice now. IMO it’s not something everyone in the group needs to carry, if one person (the guide) has it then it’s enough.
Similarly with spokes. I’ve never had to put one in during a ride. I always tell people to take a spoke if they have funny sizes or Mavic wheels but otherwise I have a box of spares and a friendly LBS.
Tyres are expensive here. They generally cost around €40-60 for a decent tyre. I think if your tyres are good before going then you don’t need to take a spare, it would save you maybe a tenner or a tenner and a half so isn’t worth the hassle for the extra baggage. The same goes for brake pads, you will pay a premium in most shops for those so it’s worth taking a set with you.
Obviously mech hangers are essential. We have had a few people on my spare bike due to snapped mech hangers. I also ask people to take spare tubes and a pump but they don’t need to take shock pump, first aid etc.
Worth saying that your guide will know their area best so I’d go with their advice. Maybe it’s an area where there are lots of problems with snapped cables or there are no good bike shops. They’ll tell you what you need.