I do carry a small and very light plastic cup - 250 ml size - I don't *actually* need it most of the time. I carry it mainly to be able to scoop boiling water out of a pot in measurable amounts into a freezer bag without burning myself.. Since it is the same size as my alcohol stove, my stove fits inside it.

I occasionally cook in my pot as well, and in these cases I like to be able to boil up and have a coffee in the cup while cooking in the pot. However that's not that usual a situation.

Strictly speaking it's a luxury item. it's one that I keep though.