My 12 year old was in and out a lot as a toddler so i became something of an expert.
I second pyjama fairies, they are brilliant.
A second adult if you can, so someone can sit with your child while you shower, you can take it in turns to get food etc.
Bring snacks for you for when your toddler doesn't want to be left but you are starving.
video calls with friends and family. They can read a story to your little one or have a chat and you can have a break.
Sometimes they give children a load of fluid in a drip in theatre in case they don't want to drink much afterwards. Check if they do that and if they do, check her nappy frequently. I assumed as my son hadn't drunk anything he wouldn't wee either, big mistake!
There are always loads of magazines like take a break etc in the parents room. Don't read them, they are full of doom and gloom. Bring a light hearted book that doesn't require a lot of thinking. I read sweet valley twins in hospital.
bring a pillow for you. Hospital pillows are rustly and there are never enough because people steal them (goodness knows why).
bring a rucksack instead of a handbag that's big enough for your valuables (phone, tablet, purse etc)
don't forget your chargers.
take a photo of your toddler in PICU. You might not want to look at it but your little one might when she is older. My son has a photobook of photos from "when he was poorly" that he likes to look through sometimes.
take photos of your little ones teddy doing things when she is in theatre. She may be a bit young for this but my son asked me when he was about 3 or 4 what teddy did when he was asleep. So i took a load of photos of him having a coffee, browsing in the shop, carrying out a bar of chocolate bigger than him etc.
sometimes by rebecca Elliott is a brilliant book for toddlers about being in hospital and also the hospital dog by julia Donaldson. I find they are realistic without being frightening. Unlike peppa pig goes to hospital where pedro the pony breaks his leg and the nursery class all go together to visit him in hospital.