Agree with all that fietsbob said except the need to carry a spare for an extended tour.
If you're touring in the USA, Canada or Europe, you're never far from a bike shop. Plus there's always fast delivery of emergency stuff by Overnight mail, Fedex or UPS. So there's no need to carry the kitchen sink on tours if you have someone at home for backup.
Certainly carry a spare tube, a patch kit, so the punctured tube can be repaired and used as the next spare, and a small piece of booting material. You'll probably never use it but it weighs nothing so why not.
As with everything you carry on a tour, balance the weight penalty against the consequences of doing without. As you get good at this, you'll find that you can reduce your baggage by almost half, making the tour that much more enjoyable. After all a few dollars to buy something in an emergency is weightless.
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