If you compress or delete any fonts, be sure to run the mkfontdir command afterward. Eliminating duplicates can save space, but watch that you are not just deleting links to the same file. Certain files grow without limit and should be periodically purged. Consider backing these up to floppy or tape and restoring them on an as-needed basis. If you cannot delete files, there are several options available for making them smaller.
Compression programs can make files significantly smaller.
The GNU gzip program provides excellent compression. It is ideal for compressing data files such as documents and source code that do not need to be on-line at all times. The best option to zip will provide the highest level of compression. If you maintain multiple revisions of files, particularly source code, then a revision control system such as RCS can save space. Only the differences between file revisions are stored.