I don't see the need for a rear derailleur, if you're using panniers there's no way the derailleur can get damaged, heck you stand a better chance getting the brake levers damaged so why not carry a set of those? Actually in reality you stand a even greater chance destroying a wheel so why not carry a spare wheel? See this sort of thing can go on and on, and it gets crazy to try to carry all the parts one might think they'll need, so you don't, nor would I carry a spare rear derailleur. The only things you need are consumables, like a spare tire, brake pads, couple of tubes. In America, which is where I'm at, if I'm doing a tour and say a tire gets destroyed and I replace it with my only spare, I know I won't have far to ride before finding a bike shop with a tire. So to carry around 2 spare tires, derailleur, etc, etc, is making your carry load heavier and taking up more space that could be used for other stuff, or to simply reduce the carry weight; you can't go on tour and be a rolling bike shop, not even expedition cyclists carry spare derailleurs though they will carry 2 spare tires because they could be weeks or months away from a the nearest bike shop, in American I would be less than a week away from one so I take my chances with just one spare tire.
As far as repair stuff I take on a tour is not too much different than when I ride locally for a few hours. So on tour I carry a frame pump instead of a mini when riding locally, but I carry a mini for back up when touring, while I might be only few days from a bike shop finding air is something I need now; I also carry a presta to schrader converter just in case my presta seals fail. I carry a spare tire, and chain lube when touring. Maps of course.
The rest of the stuff I'm going to mention is with me no matter if I'm touring or riding locally and in the seat bag:
spare tube;
Park (the only brand that works) glueless patch kit (yes I know how to make these last the life of the tube, if anyone is interested just ask);
boot patch (these are only temporarily patches);
Presta to Schrader converter;
Park MTB3.2 mini tool (great tool no longer made);
2 Soma Steel Core tire levers (I add a VAR tire lever on tour because the Schwalbe Marathon Greenguard tires are a real pain to get on);
QuikStik;
small folding pliers;
4 reusable zip ties;
2 Fiberfix spokes;
phone in a waterproof case;
3 feet of black Gorilla tape wrapped around a short pen that I can use for writing;
$50 cash (more when I'm touring plus my cr card);
spare batteries for bike computer;
several packs of hand wipes;
state ID card;
old copy of my insurance card;
minor first aid stuff;
superglue;
I think from memory that's all the stuff I carry, the real small stuff and the cards and money all fit into a specially designed Altoids tin that then goes into the seat bag (if interested I can show you how that works too).
Obviously when touring I carry stuff in my panniers (rear only, no front panniers), handlebar bag and top tube bag; along with 3 24 ounce stainless steel bottles; tent, sleeping bag, sleeping bag liner, mat, camping pillow, larger first aid kit, survival knife, couple different ways to start a fire; compass, small flashlight, compact blow up solar lantern, cookware and utensils, tiny backpacking stove, fuel for stove, windscreen for stove, extra bungee cords, dishwashing soap, biodegradable body soap that also washes dishes, 2 nylon scrubber pads, couple of extra bottles of water, trash bags, of course food, and clothing. I know I missing some stuff due to going off of memory.
I do line my panniers with a trash bag to keep food stuff from leaking onto the inside of the bag and staining it, plus keeps odors down; I also put all my food, most other things too into gallon zip lock bags to make sure nothing gets wet or nothing breaks and spills even though the bags are waterproof.
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; saddlebag if possible, or pannier(s).
