My heart goes out to you, there’s nothing worst than watching your baby go into theatre. My now adult son had his first op at 18 months I’ve lost count how many since but even now he’s 30 it never gets easier.
my to go list for his hospital stays, maybe a little out of date now, but it gives you a start
plenty of clean underwear and easy to wear clothes for both of you - more than you think you will need.
most hospitals let you take a blanket and I always too his pillow slips (teletubby). Don’t forget you might need a blanket hospitals can get cold at night.
favourite drinks / snacks
charger cable
toiletries - I always found the baby bath stuff was good for sponge baths.
fan
favourite story book
a book or something for you to read, you spend a surprising about of time watching them sleep
note pad and pen - trust me on this one
one of the best things I found for distraction is a small bottle of bubbles, silly I know but have dried many tears.