Yes, I do use consumables. The ones I use the most are Universal Resistance and Psychic Resistance for the final boss battles.
Times I used the consumables you mentioned:
I threw Holy Water on Cazador. It doesn't work very well. For giggles, I also threw holy water on Astarion, but I don't remember much happening.
I used Oil of Diminution against Grym (made a tiny Grym).
Things that I would also like to shrink:
The Ogres (to make a tiny Lump)
Red Dragon in the final battle
Ansur
Raphael
Tiny Hag
I kind of want to use the oil of dimunution on the gnomes because they're already tiny and I want to make them tinier to see what it looks like. Or a tiny cat. XD
OR. OMG. BOO. I need to get Minsc in my party, summon Boo and then shrink him *dies*