I mostly ride roads. I run tubeless, I carry:
1 spare tube
patch kit
small pump
several CO2 cartridges and valve
boot
Dynaplugs
tire levers

I've never needed the tube or of course the patch kit for the tube or tire levers. But do use the plugs and CO2 a few times per year when a large puncture won't seal. I could certainly get by without the tube etc. But, I like the idea of being almost certain I can deal with any sort of puncture without having to phone a friend. The tube etc. simply doesn't take up that much room and I'm not a weight weenie.

I pull goat heads out of my tires after almost every ride and these leak air for a moment until I spin the wheel to get sealant in there. I have a few bikes I don't ride often enough to keep up with sealant. In those cases I use tire liners, heavy duty tubes, and Slime. Still carry spare tubes etc. for those.