If you must grab a red-eye - one of those overnight flights that you always wonder the day after, "Why or why did I take that flight?" then here are a few items I suggest you pack.
Eyemask: trust me, most people don't shut off the screens of their TV sets (on Air Canada each seat comes with its own screen) so you feel like you are in a bad horror movie.
Lightweight blanket, shawl or extra sweater: unless you want to pay a couple of bucks bring one with you. They always come in handy to shut protech against any chills; to creater a lower lumbar support system or to wrap about your neck if you don't have a neck pillow.
Baseball cap: stops chills, protects your head from the person behind you, allows you to hide your face when you are sleeping and drooling.
Ear plugs or headphone sets: Again save a few $$ and bring your own headsets. Blocks out noise or at least allows you to select a audio station you want to listen to as you try to rest.
A wide mouthed water bottle (empty): I use my reusable coffee cup for water. Even on a small flight of a few hundred people, over 500 cups must be tossed on EACH flight. If you noticed on most flights the don't bother to recycle anything. I usually fill it before I board from a fountain.
Neck Pillow: Just recently I picked one up and I actually discovered that I loved it.
Slip on/Slip off shoes or slippers: Just to make those treks to the washroom easier.