1 general:: Phrase(s): pack them in Fig. to draw a lot of people. • It was a good night at the theater. The play really packed them in. • The circus manager knew he could pack them in if he advertised the lion tamer.
McGrawhill's American Idioms And Phrasal Verbs
2 general:: Attract a large audience, as in A big star will always pack them in. This idiom alludes to tightly filling a hall. [c. 1940]
American Heritage Idioms