SPOKE WRENCH!
Ooops, sorry, that's often included in many multitools. I'm just surprised how many don't know it's there, never mind when or how to use it.
Other than that, it's the usual. I'm pretty minimalist. Spare tube, patch kit, pump.
My multi-tool has a few allen keys, philips/flat head screwdriver, spoke wrench and chain tool.
In my 20 years of road and off-road riding, I haven't needed a lift due to mechanical, except for the one time I broke a Shimano chain without the special pin.
In the other, as near as I can tell, the chain snapped, derailleur bent, derailleur hanger bent, and multiple spokes broke. Everything wrapped around so badly I couldn't even roll the rear wheel, so I had to walk
I had one of that happened to me.
I was so far off the beaten path I had to somehow fix it. Or it would have been a very long walk (or very long wait for someone to come get me)
Took the derailleur off the bend hanger. Now that's out of the way, shorten the chain to some middling gear and made a single speed.
Wrangle the broken spoke out of the way. tighten up the neighboring spokes so the wheels were "kind of sort of" true (far from it). Disconnect the rear brake so the wheel will spin. No biggie, I still have 1 brake: the front brake!
Some uphill I had to walk. Some downhill I had to keep my fingers on the front brake so my speed doesn't get too out of hand.
Since I was already on the "homeward" leg, I basically finish the loop I started. Surprisingly enough, I made it to the car only 1/2 hr later than I planned. So my "major surgery" to my bike's drive train must have taken less than that.