I think rainwater capture would mostly apply to desert dwellers and shipwrecked saltwater sailors.
I guess if I had to I would use my tarp, my tent fly or some other piece of waterproof fabric as a basin and a funnel.

There is often dew even in deserts, and I have seen instructions for the desert stranded to mop up the morning dew from grass or other chilled surfaces.
There were instructions for using expedient materials for the mop too.

They say you can gather a lot by mopping it with a towel and then wringing the towel out, but again it is something I have never had to do.