For my son's 4th birthday, he decided he wanted a garbage truck cake. I made cake in three loaf pans. For the garbage part of the truck, I placed two of the loaf pans together with frosting. The third cake was cut up to resemble the front end of the cake. (It had a lot of frosting connecting the pieces :) )
I used pound cake for this so it didn't crumble as much.
The garbage can is a swiss cake roll with a Reese peanut butter cup on top. .I frosted both of them with blue frosting. The wheels are chocolate donuts with frosting and a chocolate chip in the center. The lights are twizzlers. The windows and grill in the front are Hershey bars with white frosting outlining them. The "garbage" in the back is trail mix.