Abstract: A universal packer unfolds folded open side container blanks into fully opened containers and side loads them with complements of articles. The blanks are metered by a supply station and are propelled downstream to an unfolding station. The container flaps are spread apart, and expander arms enter the interior of each blank, thereby starting to unfold it. Erector arms strike the partially opened blank at the trailing edge thereof and push the trailing edge downward relative to the blank leading edge, thereby continuing the unfolding process. Drop lug assemblies emerge from under the blank trailing panel and pivot from a horizontal to a vertical attitude while in contact with the blank trailing panel, thereby completely unfolding the blank. Simultaneously with blank unfolding, a pair of grouper mechanisms forms the complements from a mass of the articles. The complements are propelled downstream in unison and aligned with the open containers.