Pretty much all of them, except for the military and the FBI. Congress and the federal government is prohibited by the Constitution from operating within the states. It can only operate within the territories and possessions owned by the federal government. I give you Article I Section VIII Clause XVII-XVIII and Article IV Section III Clause II.
To exercise exclusive Legislation in all Cases whatsoever, over such District (not exceeding ten Miles square) as may, by Cession of particular States, and the Acceptance of Congress, become the Seat of the Government of the United States, and to exercise like Authority over all Places purchased by the Consent of the Legislature of the State in which the Same shall be, for the Erection of Forts, Magazines, Arsenals, dock-Yards, and other needful Buildings;--And
To make all Laws which shall be necessary and proper for carrying into Execution the foregoing Powers, and all other Powers vested by this Constitution in the Government of the United States, or in any Department or Officer thereof.
The Congress shall have Power to dispose of and make all needful Rules and Regulations respecting the Territory or other Property belonging to the United States; and nothing in this Constitution shall be so construed as to Prejudice any Claims of the United States, or of any particular State.
Congress and the federal government has so little to do that the Constitution specifies that it must meet once a year. This is part of the Constitution because the author's were afraid that a Congressman would actually forget to show up. I give you Article I Section IV Clause II.
The Congress shall assemble at least once in every Year, and such Meeting shall be on the first Monday in December, unless they shall by Law appoint a different Day.