I carry a Lezyne, Port-a-shop toolkit (
Lezyne - Engineered Design - Products - Multi-Tools - Port-a Shop Tool Kit). Tire pump. Digital shock pump. Co2 tire pump, spare tire, two spare tubes. A fist-sized multi-tool that has the majority of what I need to tighten a fitting during a ride. Brooks seat wrench. Rohloff wrench head. Multi-meter. Fluids and spare parts. Flex tape and the Mil-spec/Polyken 231 tape.
I love being able to pull up to anyone with a bike problem and fix it. I rode up, patched, and filled, a little kids tire once. He looked at me like Superman.