I’d say take whatever tools and bits are required to fix what is most likely to go wrong: puncture kit, chain tool and quick links, hex and torx keys. I’d bet that if you dont have a small mini pump as a back up to the CO2, Murphys Law is more likely to kick in, so a mini pump is handy insurance.
Sometimes changing a tyre is difficult down to technique and not tools. Tools can ruin rims. I was fixing a superlight Schwalbe tube last night, and took pleasure in getting the tyre on without levers. Tyre was a tight fitting Veloflex clincher and the rims are wide + tubeless ready Easton EA90’s. Its a matter of making sure the tyres are seated in the middle of the rim where the circumference is smaller. You need to practice this at home. I noted that the glue in my puncture repair kit was getting thicker and will probably dry out soon.
One way of working out whats likely to need to be fixed is to think about what you have had to touch in the recent past on the bike. I was in a sportive at the weekend and there was someone who clearly hadnt adjusted his gears in a while and was struggling with shifts on a particularly steep climb, who then fell off. Guys were walking this climb. The consequence of bad shifting on a tough climb is potentially a snapped chain.