My son insisted on a fire truck cake for his 3rd birthday. I found some ideas here, then figured out how to do it myself.
I used one box of chocolate cake mix (with one extra egg and a teaspoon of vanilla to make it taste more homemade) to bake two loaf cakes. I cut one loaf in half. I placed the cut loaf flat side to flat side, and frosted them together and added a couple of toothpicks to stabilize them.
I placed the whole loaf on the back side of this. In hind site, I wish I had used a knife to cut the domed tops off the loaves so they would have stacked better. Because I didn't know to do this at the time, the front loaves had a hard time staying together, so I had to do a couple of patch up jobs with frosting as the day went on.
The cake was set on a platform of wood covered in foil to give the truck a little "lift". I tinted homemade buttercream frosting with 2/3 of a bottle of n taste red gel dye. I frosted the whole cake red. I placed some white icing in a decorating bag with a tip 3 and made the ladder on the topside of the back of the engine, the white line about an inch up from the bottom of the cake, a number 3 on the front and back of the truck, and the windows.
I used the basket weave tip (I can't remember the number) to fill in the windows and to do the rest of the details. I put the chocolate sandwich cookies on with big globs of frosting. The pipes on the side of the truck are black licorice. We used red and yellow dot candies for the lights and M&Ms for the gauges.
The cake was a hit! My son thought it looked cool and that is all that counted!