I showed them my driving licence, but to be honest they didn’t ask for anything.
But is good to have something to prove your identity.
The nurse told me to bring something just in case.
And yes, water only, and just few sips as Kelbel mentioned.
What I did to forget about thirsty and hunger that morning, I took a nice movie with me on my laptop, so I watch it in the room at the hospital. It will take your mind off for a while…