I hardly ever use my healing potions, I feel it's a "waste" and end up with several stashes of 20+ scattered around different levels. I'm guessing at least 1/2 of my really good character deaths could've been avoided if I'd just taken some potions.
I'm pretty sure you can't wish for a certain liquid. If you wish for a bottle of something, it'll just give you a bottle with a random liquid. Try wishing for dozens of bottles, i bet you find a sulphuric acid one eventually.