Myself a scanner is a must on every train trip, my wife want's to throw it out the window though
The one I take with me on trips is a very basic Uniden portable scanner that is about the same size of a cordless phone. I purchased it about 8 years ago at Service Merchandise (now out of business) for about $90. It's a 10 channel model, meaning I can only program 10 frequencies in it, which is plenty good enough for train listening. It can also run on 4 AA batterys or normal 110 volt current.
A good store to check out would be Radio Shack. I am sure that you could find a very basic & good quality scanner in about the $100 range.
It does help to know the basic language of railroading. The first time listener may have trouble figureing out what the meaning is of certain things. Example (engineer talking) " Amtrak #30...East #2.. Approach, turkey foot.. 30 out". The meaning of this just to use an example would be this..
Amtrak #30 .... The train your probably on.... the Capitol Limited.
East #2............... Your traveling Eastbound on track #2
Approach......... The track side signal is showing an "approach" indication.
Turkey Foot..... The interlocking or block name that the signal is protecting.
And no I didn't make this name up...It's a real interlocking
on the Capitol Limited route.
30 out.............. End of transmission
Getting to know what the meaning of different signals are, and other railroad lingo, you will be just as informed about the train as the engineer and conductor. People often look at me weird on a train because I will turn to my wife and say, were slowing down or were stoping seconds before the train will actually take action to slowing speed. I always wear a headphone, this is a must when sitting in coach, but not sleepers. So make sure your radio has a jack to plug headphones into.