My cakes usually go on one of a couple of different plates that are a few inches larger than the cake and then into a box that the plate just fits in (so it doesn't slide around). Sometimes I put a bowl over the top (bigger than the plate, not resting on it) or plastic wrap and toothpicks, but usually just the box.  Works fine unless you forget about it and leave it in the back of your friends car on one of the first hot days of spring:)