Depends on the type of tour you are doing. My 20 mile work commute requires panniers, cold and wet weather gear for the winter, lights for early morning and late evenings along with the common small items:
1. Two spare tubes
2. Patch kit
3. Bike-specific multi-tool
4. Frame-fit pump
5. Emergency identification
6. Water bottle with water
Regular ID, insurance info, cash, phone, clothing, keys, safety equipment, bike lock, shoes to fit my clipless pedals, and other items taken for granted are assumed to be on the list. Ziplock bags for anything that can't get wet may also be added to the list.
I choose to use a GPS enabled cycling computer for courses and routing. On my tour from Maine to Florida, I carried significantly more. For closer to home touring, one can go a long way with little more than a patch kit and a pump.