When my Daughter had a GA I was told small sips of water were fine. I was also told the main reason is to prevent vomitting.

I kept my girl up late gave her the last snack at 10pm then let her sleep in right up until I was ready to go - luckily we were 2nd on the list so once we arrived we didnt have to wait long for her op so although she did ask for something she didnt get too distressed when I said no.

Good luck with it. Make sure you have someone with you on the day to distract you. I went into RCH on my own and I was pacing the whole time she was gone- I needed someone who could of distracted me and passed the time faster (her op took longer than grommets take).
Sjl