Gum.

One of the surprises we gave the kids throughout the train trip was gum.  It's funny how something so simple can really get them excited.  Of course, we also had it to help with the elevation gain.  Lucas understands not to swallow gum but we really had to talk with Sophie beforehand about "spitting it out when you're done!"  Here's a conversation I had with Sophie about 5 minutes after her first piece of gum.

Mom:  Sophie, where's your gum?
Sophie:  (blank stare and shrug)
Mom:  Where did it go?
Sophie:  Down my froat and into my tummy.
Mom:  Oops!  You were supposed to spit it out when you were done with it!

Sophie:  I did.  I spit it into my froat!