I always carry:
- Spare tube.
- Tube patch kit.
- Small multi-tool for bikes.
- Tire levers
- Mini-road morph pump.
- Water bottle or two.
- ID, Health Insurance card, Credit Card, $20 cash.
It all fits into my small seat wedge, except for the pump which attaches under my port-side chainstay, and my water bottle(s), which obviously fit to the frame.