Ear plugs. More ear plugs. Ear plugs. Hospital wards are noisy places even at night. Maybe also an eye mask if you want darkness.
A distraction for if you're feeling too groggy/weepy (anaesthetic and painkillers can do interesting things) for reading. Magazine to flick through, music to listen to, downloaded films/podcasts to watch/listen to (and noise cancelling headphones)... Puzzle books, a notebook if you want to write things down (either feelings or what doctors are telling you or questions to ask the staff the next time they appear).
If you're feeling anxious etc then have you got something comforting to take? A soft blanket and/or your own pillow? The scarf suggestion by a pp could also work for this. (Can someone bring you in a pillow after you're on a ward if it doesn't fit in your bag? Can help you feel more comfortable / less miserable depending on how you're finding things/meds are hitting you.)
Do you know if you'll be expected to shower at hospital before you're discharged? If so, flip flops and a plastic bag for life to chuck your stuff in so it doesn't get wet can be helpful.
Toiletries. (Scents that are familiar and homely can help). Baby wipes if you're struggling for the first day or so. Dry shampoo maybe if it's your thing.
A few photos of loved ones?
Some people like slipper socks instead of slippers in hospital because it makes it a little easier when bending and moving isn't as easy (maybe ones you don't mind getting trashed...). I prefer loose slip on shoes instead of slippers (so no bending when getting dressed to go home, less stuff to carry, doesn't matter what the floor is like esp if you have to walk to theatre).
Comfy, stretchy clothes for going home (and during the day if you're there for the longer scale and want to have a bit of normality).
Peppermint tea is something lots of people say they found invaluable.
Handheld fan if the ward is hot / you are hot. Moisturiser if the hospital environment dries your skin out.
Some of your favourite biscuits or snacks for in between meals if you want them. Somebody to bring you food if the hospital food sucks?! (Even if it's just picking you up a tasty sandwich!)
A nicely stocked freezer of meals at home. The things you'll need when you get home ready at waist height (no stretching or bending needed then). Nice things ready and waiting at home for you. Family and friends primed with specific ways to help. Over the counter painkillers stocked at home.
When it comes to showering at home, one of the best tips I got from an OT was to have a towelling robe specifically for showering so if you're struggling with fatigue (as you probably will for a little while) you can wrap yourself in that after showering and just go and lie down until you've recovered enough from the exertion of showering(!) to get dressed. It is also easier to wrap yourself up in one to dry yourself when you're tired (but not "rest immediately" tired) and sore as it is a bit easier than using a towel and no awkward stretching or twisting involved.
Can help with nerves to know things are ready and waiting for you at home, and can also ease any emotional rollercoaster experiences afterwards.
Good luck.