@Rachox,
When I was in hospital the most irritating thing was the HCA wanting to test my blood glucose at silly times. There was no rhyme or reason to the timing, just someone somewhere had decreed that it should be tested 4 times a day at random times. What bothered me most was that she went from patient to patient with the meter and test strips, never washing hands or wiping the meter between patients. I refused to allow her and got my own testing kit brought in. Of course, labelled 'non-compliant' thereafter.
As for hospital food, it was carb heavy, but you already have been given some excellent suggestions as to alternatives. I found it useful for whoever was visiting to bring in individual meal size container of salad, meat, hard boiled egg, cheese or yogurt. Kept some small pots of nuts, and individually wrapped mini cheeses for if I felt hungry. I seldom did. Anaesthetic is a good appetite suppressant for me, as is having to eat in bed.
As you are going to, hopefully, be in just one night, possibly you will only need something light the evening of the surgery, (perhaps, depending on time of op you will be sleepy and not needing to eat until following day), then breakfast and lunch the day after.
Can a visitor bring those to you?
Do remember to drink plenty to keep hydrated post surgery, and don't worry if you need a day or two without your usual low carb management regime. You have done so well since diagnosis, a couple of days should not do any harm to that management.
Best of luck with it, and wish you a speedy recovery.