Most important govdoc reference sources

What are the essential 3-5 print Government Document reference sources that you can't work without in answering reference questions? Diane Kovacs posed the question to librarians on Govdoc-l, publib, libref-l, LIS-LINK, DIG_REF, ERIL-L, Buslib-L LawLibRef, Law-Lib@ucdavis.edu, LawSource, and the results are posted here.