Whenever I carry fragile food items such as eggs and bananas I try to be a little more careful on how I ride. Carrying a birthday cake sounds like a challenge, those things are so soft and fragile...One time few years ago I was carrying few cans of beer packed against one another in my rear trunk bag. The trunk bag was old and the fabric was worn out in some places and padding was very thin. Two of the cans rubbed against one another and also rubbed against the rack rails while I was riding. Next thing I see was beer all over my rear wheel and frame.
My bike smelled like beer.