Money for cafe stops – entry is cheaper than a sportive but cafe controls balance that out.
Something waterproof to keep route sheet and brevet card dry. Pencils for writing answers to info controls down.
Two tubes, levers and pump, charged mobile phone, clothing as appropriate. Water bottle, chewy bar for emergencies.
If the distance is new to you, go off steady. Quite common to see carbon worshipping Mamils being leapfrogged by old codgers on ancient steel tourers. There will be at least one stand out character or moment that will make you chuckle. My favourite was an older couple in a tandem with a fresh looking pheasant strapped to the rack.
Where are you riding? Need to pull my finger out and enter something before the year disappears completely