My daughter decided my son would like a truck cake for his birthday, and after looking at the great ideas on this site, I decided a fire engine would be the way to go.
I baked two cake using recipes that were orginally for bundt cakes, so very sturdy. One was in the 13x9 pan, the other in two loaf pans. The 13x9 I cut into equal 3-inch thirds length-wise, and trimmed the ends and edges so it was rectangular. This part was the "trailer" part of the truck. The loaf cakes I cut in half and used 3 halves stacked for the cab. I used one of the leftover bits to do the connecting part between the cab and trailer.
I frosted the cab in white, the connector in gray, and the trailer in red. One hint for making red frosting -- add a couple large spoonfuls for cocoa powder to the frosting. It won't be exactly chocolate frosting, but will have a chocolatey taste. This is mask any sort of bad flavor the food coloring has, and give a slightly darker base for the red to start out with, lessening the chances of it seeming pink. Also remember that the red will darken, and what looks pink while the mixer is going will often look perfect 15 minutes later. After using one (1-oz) bottle of coloring, wait at least half an hour before opening up another bottle.
After frosting the fire engine, I used graham crackers for the windshield and back (of the cab) window, oreos for the wheels, gumdrops for the lights on top of the cab, mini M&Ms for the control panals and grates (front of cab and back of trailer), chocolate pieces for the doors (I planned to use plain Hersey's, but we had a Symphony bar open so I just used that), and pretzel sticks for the ladders (one on each side and one on top). I also filled in the blank spots on the top and sides with my son's initials.
I am a baker and I do decorate cakes, but this was my most ambitious project yet. Definitely not professional, but it wasn't difficult, was fun, and was appreciated at the birthday party!