I would lean towards taking two spare tubes and leave the spare tyre at home. I'm not sure I'd take spokes either but that's because they would be of no use to me, I ride not fix. by the sounds of the miles you log a century should be no issue. Even if your longest ride to that time is 75 miles you should be fine. I like many others found the 60-65 mile mark the toughest, after that the miles don't seem as bad.