With lists of items it is often a given that they are abbreviated. Sometimes they will follow a leading sentence, for example:
In my spare time I go:
You could take any one of the activities from the list and tag it on the end of the leading sentence, remove the colon, and you'd have a grammatical sentence.
With statistics, this ...
"post office" and "postal service" are compound nouns. The former is made up of two nouns: the latter an adjective and a noun.
When both an adjective and a noun would work, there is a (sometimes quite strong) preference, and the final noun seems to determine which form is preferable. For example, we talk about a "law office" or ...