I would say the most important ones are
1. Tire patch kit and some type of inflation device
2. Cell phone
3. Credit card.
Those last two can get you out of just about any situation. Other than that I have the basic tool kit that came with the bike but I have no illusions I would know what to do with it. Unless you know what you are doing carrying a full toolset is kind of a waste of time. Carrying spare fuses can be a good idea.
If you are going on a long trip then having good maps is certainly a good idea. Assuming you are heading off the beaten path then its very easy to get turned around. And if its an extended trip then having names/addresses/phone numbers of dealerships for your bike could be a life saver. If you break down and need a tow somewhere it helps if you know where to go.
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