Ear plugs, eye mask, noise cancelling headphones, saline nasal spray (counters dry cabin air), sleeping pills (see your doctor beforehand for something suitable that won't give you a sleeping pill "hangover").

I always like to bring my toothbrush and paste on long flights as it helps me feel a bit fresher.

If your airline allows, you may be able to select a special meal which means you're guaranteed to get your meal first before the main meal service. I have in the past had a "high fibre meal" and it was good because I had fresh fruit instead of a stodgy cake dessert, and I felt much better for it.