Comfortable? Hmmmm... Maybe we weren't clear on how big this surgery is. Not anything you can bring to make the patient much more comfortable.
Slippers would be good because you need to walk, walk, walk. A robe to slip over the hospital gown when you walk would be good. Other than that, not much.
The person there with you should bring comfy things, reading materials and/or silent video games or something else to keep themselves occupied because you will be in and out from the pain meds. They will also need to bring patience. Sometimes, the pain meds can make people act weird so a sense of humor for the caregiver is important. That's important because it makes you more comfortable because they don't whack you upside the head when you say some morphine induced nonsense.
Good luck with the surgery. It is really tough but it is worth it in the long run.
Did I mention that you need to walk at least three times a day starting day one? The more you walk, the faster you get better and get to go home. Chew gum after the surgery as it has been shown to help get the intestines to wake up sooner. Stay on top of the pain but don't ride that pain medicine button so hard that you have zero pain because the pain meds can prevent the intestines from waking up. Expect to feel like a truck ran over you and then decided to back over you and do it again. Know that even though you feel that way you HAVE TO get up and walk and that you WILL get a million times better in a matter of steps. Steps, not time, are the key to recovery.
Mike