Map packages (.mpk) make it easy to share complete map documents with others. A map package contains a map document (.mxd) and the data referenced by the layers it contains, packaged into one convenient, portable file. Map packages can be used for easy sharing of maps between colleagues in a work group, across departments in an organization, or with any other ArcGIS users via ArcGIS online. Map packages have other uses, too, such as the ability to create an archive of a particular map that contains a snapshot of the current state of the data used in the map.
If you have ArcGIS 10 give packaging a try and here’s a tip:
Before packaging a map, be sure to enter descriptive information about it in the Map Document Properties dialog box. This information is built into the package and is accessible to others when you upload your map package into ArcGIS online. You can access this dialog box by clicking File > Map Document Properties on the main menu.