I also suffer from migraines. I find that sinus problems will trigger migraines just about as fast as cabin pressure - or maybe they're related.

I usually take Sudafed before and during any flight longer than 3 hours, and I've found that it seems to help tremendously in preventing the migraines.

And I don't do ice packs, I prefer the opposite - moist heat. A ziplock baggie with hot water across my face can relax me in a heartbeat.

Another trick is to put my head completely under a blanket, just as another passenger did. It has been suggested that reducing oxygen intake will force your constricted vessels to open up, thereby helping to relieve your headache. It seems to help with me.

Caffeine can also help, if you can tolerate it. Try drinking a cup of coffee. If you can't keep it down, sipping a Coke might be better.

I was diagnosed with migraines at the tender age of five, long before there were meds that were appropriate for me. So I learned all the little non-medicated tricks at an early age...