The New York Times brings the news of a (likely) underreported problem from the holiday season: rats gnawing on edible packages of goodies in the post office. In the example cited by the paper, a rodent was able to consume an entire brownie from the Vermont Brownie Company. The lesson here is to put as many layers as possible between your food and the outside of the package. It will reduce the likelihood that creatures can gain access to the food.
Also, inspect your package once you receive it to ensure no tampering is visible. There is also direct video evidence that rats love ice cream.