This keyword takes a list of packages to be retained. All packages in the list are kept in the delivered image, regardless of the values of the :smash-packages and :delete-packages keywords.
If :packages-to-keep is :all, then the two variables above are set to nil. See also Coping with intern and find-symbol at runtime.
Note:
Other keywords push packages onto the :packages-to-keep list.
Note:
When you keep a package by :packages-to-keep, this does not cause that package's symbols to be kept. To retain symbols, see Ensuring that symbols are kept.
LispWorks Delivery User Guide - 15 Feb 2015