If a system has particular requirements that a package always be included in %packages (for example, a hardware-specific package that is needed for booting) then it may be useful to add the package to a per-system snippet on the lab controller. I think we used to have this with the rhts_packages snippet but it got lost along the way with commit a6a65e05.
On Gerrit: http://gerrit.beaker-project.org/1444 Beaker admins will be able to create a file like /etc/beaker/snippets/per_system/packages/hostname.example.com containing extra packages that are needed for that particular system.
Verified with build 0.9.4-2.git.104.1433411. By creating a file named /etc/beaker/snippets/per_system/packages/$(system_fqdn) which containing some extra packages, the kickstart file will be generated with these extra packages appended in the "%packages" part. And verified these packages were installed after the install task.
This has now been released