Generally they give normal saline through an IV depending on your hydration status. They would give some sort of dextrose if they were trying to "pull" water from your cells. If there is any weight gain it would probably be from having your fluids run fast during surgery. That's typical. After a few days you should be getting rid of all the excess water through your urine.
That is awesome about your husband bringing your foods to the hospital, what a guy
I would ask the doctor about the diet that you are on and make sure it will be able to be followed during recovery. Wound healing relies on protein which you may be getting enough of but a multi-vitamin wouldn't hurt if your not already taking one.