I have some arthritis & stenosis in my neck so support is very important when I am holding my neck upright for extended periods of time (like flying).

So, I use a cervical collar like:

http://www.mohawkmedicalmall.com/Mer...de=PRC%208309x

I know this looks extreme but it does support the head well and these collars have velcro on the back which can be undone so the collar becomes a strip - much easier to pack.

Side benefit, people are incredibly gracious when you where one of these. I don't wear it all the time but when I feel my neck straining, it helps alleviate the stress on the neck muscles.