It is a long surgery, so consider eating a meal in the cafeteria or bringing sandwiches
try to keep it healthy, you will feel better for it and so will your body. Carrot and celery sticks with a hummus dip (that you make) string cheese for protein, apple wedges with a peanut butter cup. If you are going to be in a public waiting room, there is a chance of bored kids clamoring around you when you pull out the snacks. Most hospitals have an out of the way waiting room, ask the recovery desk volunteer to guide you, if you prefer more privacy.
It helps to plan something besides waiting at the hospital. If there is to be a group of you, one group can leave for a few hours, go shopping, go out to eat, go to a movie, etc.
Then the other group can go out when you come back, It sure helps keeps the spirits up, it can get very boring and tiring, to sit for hours and hours. Sitting in a waiting room full of others who are waiting for loved ones to come out of serious surgeries can be very stressful, because you all get to talking about the surgeries.
Can you tell I volunteered in a hospital for many years? I saw how other families handled the waiting situations.
I hope all goes well for him.