This is a contentious issue with no conclusive answer. A lot will depend on your itinerary. If you're cycling to distant corners of the world away from civilization, it's critical that you can solve a wide range of bike problems on your own. Many bikers may bring various tools and spares on such journeys. If you're cycling through developed towns and cities, you'll almost certainly come across bike stores frequently. This means you can reduce the number of items on your bike touring packing list. I believe a bare minimum of bike tools should be carried on any multi-day journey (or even a day cycle).