Don’t go cheap on the socks, or underwear.
Light weight thermals (breathable).
More than light weight thermals (breathable).
I guess the below are not really work clothes.
A few notepads you can carry in your pocket to you know, take notes right then and there.
If allowed, an iPhone or something like that. You can’t take it every places, and some places you risk damaging it, but the ability to take a picture of certain things can help a lot. And when you can’t take that around, that’s what the notepad is for.
A flashlight you can hold in your mouth, something along the lines of a single AAA battery size. It does not need to be some nuclear powered intensity either.