I'm just a commuter and around-town rider, though I sometimes go on longer weekend rides. After 40+ years, I've got a pretty good mental inventory of what's likely to go wrong. Maybe I don't break things because I'm not a particularly strong cyclist. These days, my kit contains:

The means to fix a flat. In my case I prefer to have a spare tube plus a patch kit, so I can decide which one is more convenient at any given moment, for instance if I'm running late for something, or it's raining. I've had multi-flat rides in the past. And while I still carry all of this stuff, I haven't had a flat since I upgraded to puncture resistant tires on all of my bikes.

Allen wrench set. On my rattly old bike, some things tend to come loose such as the fenders and rack.

Spare blinky.

Truth be told, I carry some things in case someone else in the family has forgotten theirs, such as the blinky.

In my view, keeping up with maintenance at home is the secret to reliable service while out on the road. I do all of my own repairs, so I'm familiar with the ins and outs of my bikes.