The $20 I spent at Brookstone to get a travel pillow was money well-spent.

As for otherwise, do check-in at a kiosk and try to grab an empty row, or at least one with the middle seat empty. That empty middle seat makes a world of difference to me on the red-eye. (One reason why I avoid 767s on red-eyes; much better chance of an empty middle on a 737/757). Otherwise, I'd just bring a book/laptop/DVD player and relax.