I commute daily (on S.E. Pennsylvania's SEPTA, not Amtrak) and I find three items in my pack to be invaluable to my sanity:
1. Bose headphones (the full over-the-ear kind)
2. My iPod
3. Earplugs
Put in the earplugs, set iPod to play "Rain on a Tin Roof" (the 'white noise' version -
http://www.amazon.com/Rain-On-a-Tin-Roof/dp/B0012A0KH0 , not the Julie Roberts song of the same name). Plug headphones into iPod, turn volume to max. You can just hear the rain through the earplugs.
Yesterday I looked up from my book and saw the woman next to me yakking into a cell phone. I couldn't hear a thing she was saying.