Depends on the type of surgery. This may seem delicate,hope not to offend but really panties in a larger size are a luxury when you can't reach to pull up, when your body bloats after surgery etc. A soft gown to wear after the hospital gown is no longer required.
A pretty pillowcase.
A small pillow to protect body from seat belt and to use to sleep with, again depending upon the surgery.
Prayers for your dear friend. A prayer shawl would let her know others are praying. If you don't have time to whip one up call a local church, put her on prayer list & ask if they have a prayer shawl ministry.