One of the good things about a bike is how easy it is to fix it. Flat tires and broken spokes are the most common problem. Within the biketour community, we are carrying some parts, which can be communally used.
Try to bring things in any case, which your bike requires: correctly sized inner tubes, spokes and brake shoes, pump and basic tools for your bike.
Other things highly recommended: chain oil, bike lock (don’t forget the key!), rain protection for you, the bike and your equipment on it, lights (front and rear), water bottle holder.