1. A computer-implemented serialization system that serializes file system items and associated entities of the file system items to generate a serialization stream, the serialization system comprising—a processor and one or more physical computer readable storage media operatively coupled to the processor, the computer readable storage media having stored thereon computer executable instructions that, when executed by the processor, implement the following components: an identification component that generates identification information identifying a file system item from within a file system store, the file system item including one or more properties that further define the file system item, the identification information also identifying associated entities of the file system item, the associated entities including: an embedded item that comprises at least a second file system item; an extension that extends the file system item with at least one additional property; an item fragment that identifies the file system item as part of a collection; a backing file from which at least a part of the file system item is promoted; and a serialization component that employs a serialization option to select a subset of the associated entities to include as part of a serialization stream, and, in response to receiving the identification information from the identification component, serializes the file system item and the subset of the associated entities to generate the serialization stream, the serialization stream including: a serialized serialization length that specifies a length of the serialization stream; a serialized file system item; a serialized subset of the associated entities; a serialized header that includes serialization information associated with the file system item and the subset of the associated entries, wherein the serialized header is generated by the serialization component and facilitates random access to the file system item and the subset of the associated entities; and a serialized header offset to the header and which identifies a location of the serialized header within the serialization stream.