Buckleupdorothy's suggestions sound pretty spot on to me!
I completely agree on the carry-on. I always make sure to bring books, magazines, some Sudoku puzzles etc.
Because temps can differ between planes, airports etc. a light sweatshirt or jacket is definitely important. I usually prefer a zip-up or cardigan style so that I can drape it over myself like a little blanket if I get cold.
An empty fillable bottle for water is definitely important as are any essential medicines, tylenol/aspirin or similar in case of headache, and some snacks.
If it's an international flight or a flight with multiple connections I'd recommend bringing a spare change of clothes (or at least underwear and socks) in case you arrive before your luggage.