A package for reading and writing ZIP archives as BLOBs published by Anton Scheffer compress-gzip-and-zlib.
Other than splitting into .pks and .pkb files, the only change I made was declaring the package to use invoker rights (AUTHID CURRENT_USER). The reason is that it can write a file to a directory and that priviledge should depend on the caller.
Somewhere along the way I picked up a version that added an optional Date argument to add1file. It is a slight mismatch from the above link. Seems useful though. If you already have as_zip installed without it, you might choose to remove the optional date argument from methods in app_zip.