It's not always so easy to get a ride or a taxi, especially if you're out in the woods. It can be a long walk. It always works out, but having equipment to cope with minor errors is a good idea.
Good to have with you:
Hose(s), pump/Co2, extra chain lock, chain breaker/Multitool, team patches (Park tool GP-2 kit and patches of glue sandpaper from Parktool VP-1), extra gear lug, some cable ties, With that kit you can do most things. I also have some Gorillatape that I wrap around the CO2 cartridge. A file for tires is good to have, so if the hole in the tire needs to be repaired, you can file it up. I also have a tool to be able to open a chain that has QL, mine is part of a larger kit, but there are several options.
Feel free to complete with a tool to plug a tyre, if you drive TL (tubeless). Stan's DART is the best. Park Tool TB-2C Tire Boot, for repairing tires. An extra screw for the SPD pedal is also good to have, preferably a whole SPD block, 2.5mm HEX for the pedal and a Torx, good for opening a worn screw. Tubolito are awesome extra tubes, if you ride them, remember to bring team patches for Tubolito, regular ones won't work. One piece of chain and TWO quick-links, can solve problems with broken chain. An extra valve core and tools for these, i.e. a valve core tool. Best is Stan's.
Fluid and energy in some form, and please plan (at least) a snack along the way. It splits the tour and is very nice. It is a good idea to bring reinforcements, especially in spring and autumn or if you are climbing at higher altitudes (a rule of thumb is that it gets about 1 degree colder per 200m of altitude). A warmer hat and a rain/windproof jacket are golden if there is a shower or headwinds.
Medkit in some form, good to have antihistamine, and alvedon and ipren. Takes no place, in Tuscany we cycled into a wasp nest, it can happen anywhere, antihistamine, is gold. Painkillers can help someone who is in pain. Better that the medkit is included than that it is too big. Plasters, bandages, some kind of antiseptic, e.g. you can go a long way with this canvas.