Got many great ideas from other train cake posters (thanks!). Baked one rectangular cake and one circle cake (one box mostly did the trick). Cut the rectangular one in two and used that part for the long ends. Cut the circle cake to make the rounded turn of the train track. Put this all on a piece of cardboard covered in tin foil. They sell these uncovered for like $2 at the party stores or you can just cut a piece of strong box up. Needed a little more cake at the rounded turns so the cars weren't tilting off but only had mini snickers so stacked two at each curve (8 total) and covered those in icing (yummy surprise but more cake probably would have done the trick as well). Hate black licorice but found chocolate Twizzlers at the grocery store which made great tracks on top of the Kit Kats folks recommended, and looked prettier! I put toothpicks into the ends on the bottom of the Twizzlers and then pushed them down into the cake so the tracks would meet up and not slip off once the train cars were on top.
I used the Nordicware Train Cake Pan with a little Baking Pam and everything came out great (we also make banana bread in it which is a hit!). We went with a snowy white icing theme to highlight our cool train tracks. Sprinkled some sprinkles on there only because kids like sprinkles and they were helping. Sliced a little off the bottom of the train cars with a large knife to make them flatter for the tracks. Let kids decorate most of 'em, so not winning any icing awards but they had tons of fun! Bought one black spray can of icing and used the black for the smokestack and some of the piping.
My son wanted Percy, not Thomas, but no one sells Percy stuff and my first Percy face was a disaster. So I bought a sheet of those little candied Thomas the Train faces from a party store and carefully covered the blue Thomas candy dots in green. They looked the same and despite the rest of our icing job, everyone knew who it was supposed to be. We used teddy and animal graham crackers for the outside of the animal cars and filled others up with M&M's. Used M&M's as the wheels, too, attached with some icing, but not sure those are the best looking wheels. Mostly I had to let go, and realize it was more fun to let the kids do the decorating. They loved making it and eating it and despite the amateur look, all my friends were impressed anyway!! Another kid now wants a basketball court cake with players dunking...I'm afraid the bar has been raised too high (help!).