A photocopy of your rail pass won't help, but forking over the $10-15 for railpass insurance will!!
You can keep copies of your important documents in a "secure" place in your backpack, but personally-- rather than run the risk of my bag getting stolen and some creep having access to all that personal info IN ADDITION to all my stuff, I prefer to scan the copies and email them to myself before leaving. That way you can access them at any internet cafe.
In addition to my passport, I also copy/scan my plane tickets, birth certificate, social security card, driver's license and any credit / bank cards I might take with me. I also email myself the phone numbers of appropriate institutions like banks and embassy addresses just in case. (On the other hand, I already have my passport number and all of my card numbers memorized, in addition to the telephone numbers. That helps.) Maybe that's being a little over cautious, but you know what they say about paranoia... you only have to be right once to make it all worthwhile.
Photocopies, what do I need?
There's a railpass insurance? Wow i didnt know that.
Usually,i follow tours,so the travel guide will keep all of our passports and visas etc.