Copying files from the plugin directory plays a part in the solution but is by no means the be all and end all. For a start, sometimes the plugin is OS-specific, so it might contain DLLs (windoze) or shared libraries (UNIX). Any such plugin has to be obtained on the target machine somehow.
One of the main challenges of installing your own plugins without using a network connection is that you will have to chase down any dependencies. By default, eclipse does not tell you when there is a problem installing plugins but you really do need this information. Here is what you do:
create a file called .options which contains:
then enter this command:
./eclipse -clean -console -consoleDebug -debug ./.options
This produces output that tells you what troubles it had loading plugins.
Under the eclipse directory create a directory called dropins. It should be a peer of plugins and features. Below dropins create eclipse and below that create plugins and features.
For any plugins that are missing, copy them from a windows environment that has them. They can be directories, files or a combination of the two. Be careful to copy to the correct target directory, either dropins/eclipse/features or dropins/eclipse/plugins depending on where it comes from in the source. To copy them, using WinCp. This is often allowed in a corporate environment.