*Make sure the cake won't slide, either in the box, or in the car. If the box is bigger than the board and the cake might slide, use some non-slip drawer liner. Place the box in a position in the car where it won't slide.
*Leave the cake in the freezer or fridge right up until the moment of departure. Keep the cake out of direct sunlight during transport, and use air conditioning in warm weather.
*When driving, follow these rules: Slow start. Slow stop. Slow turns. This minimizes force on the cake.
*Always, ALWAYS bring a decorating bag full of each color used on the cake, as well as your spatulas of varying sizes and one of each tip used in decorating the cake. Be prepared to make repairs, hopefully not surgery!
*Make sure you know the exact location and have good directions for your destination before you leave.
The absolute WORST delivery I ever had was working at the King Soopers bakery in Denver. My manager decided that, on the hottest, most humid day in July, I was the best option as deliverer. Full knowing I had no working air conditioning in my car. With the cake thawed out 6 hours in advance. Without working directions to the Denver Botanical Gardens (took me down the wrong way on a one-way street). The cake was entirely destroyed when I arrived an hour later. All the frosting from the sides was completely melted off the cake. I had to redecorate the whole cake as best I could with a plastic knife, and then run like heck. I wasn't even the original decorator who made the cake. It was horrifying.
However, this delivery on Friday went like a dream. Near polar opposite. I knew exactly where I was going. I had excellent air conditioning. It was 77 degrees in a September evening, the coolest day all week. I walked right in, set the cake on the table, followed the last cardinal rule of cake decorating, and gave the bride some simple instructions on how to cut her cake. Total time: 45 minutes.
The Cardinal Rule of Cake Decorating:
Take a picture of your cake
This may seem like a simple thing, but really, it's pretty essential. A) You need to keep track of your awesome creations in a personal portfolio. B) You have to have proof of what the cake looked like when it left your hands. Think of it as insurance.