Yes, I carry a TPU tube. Not because I don’t trust my tubeless setup but as a good luck charm of sorts. I believe in the Sam Gamgee rule of preparedness: “You’ll want it, if you haven’t got it”. That is, nature will inevitably send you the mechanical you’re not prepared to fix. And a TPU tube is not that big or heavy.
Yes. You’d be crazy not to, IMO. Plugs are great (I carry those too) but they rely on your sealant being fresh to function. Even though I refresh my sealant every few months, I don’t trust it. I trust that my tube (which I check regularly for integrity) will get me home.
I carry a dynaplug, a pump, a tire boot, a Tubolito tube, and a small rag to help with the sealant if things go south.
When I bikepack with a group someone will carry a small bottle of sealant and a few people will carry some CO2 cartridges to help re-seat tubeless if needed. Usually on trips I’ll carry 2 Tubolitos - small and light insurance policy.