Going to a long bike ride, remember that you are waited back home. The trip can end up late at night and far from the city, so this is mandatory to wear helmet and that your bike is in order .
It is also worth having money for food and travel in public transport (in extreme cases by taxi).
We quite often go radial routes with the finish in some city and return from there by train.
As practice has shown, it is highly desirable to have lighting devices and an additional battery to recharge the head lamp/phone/navigator.
Highly recommended to have a comfortable reflective clothing, preferably light, for night on a dark road cyclist see better.
Do not forget the repair kit, mounting, pump and at least two cameras, and preferably three.
A few words about food:
Water (preferably isotonic) is required to take! Bars, gels, sandwiches at their discretion for support machine we do not and are unlikely to appear. As a rule, trips end at the station, where there are all sorts of cafes (there is some risk to spend the way back with "adventure"), just stop on the route, where you can eat. A couple of day trips will show which set of food is more suitable for you.
Everything else is optional.