Guarantee Paychecks for America's Military Families Act - Prioritizes, in the event that the public debt of the U.S. government reaches the statutory limit, the following obligations over all other obligations: (1) the Secretary of the Treasury to pay with legal tender the principal and interest on debt held by the public; (2) the Secretary of Defense (DOD) and the Secretary of Homeland Security (DHS) to pay members of the Armed Forces the earned pay, allowances, and other compensation paid from military personnel accounts; and (3) the Secretary of Defense and the Secretary of Homeland Security to carry out a contingency operation (as defined in existing provisions of federal military law), including the pay earned by civilian employees of the DOD and the Coast Guard serving in a combat zone (as defined in existing provisions of the Internal Revenue Code of 1986).

Appropriates to the Secretary of Defense and the Secretary of Homeland Security, for any period of lapsed appropriations, such amounts as may be necessary to allow such Secretaries to provide, during the period of lapsed appropriations and without interruption: (1) pay and allowances to members of Armed Forces, including reserve components thereof, who perform active service during the period of lapsed appropriations; and (2) pay to civilian employees of the DOD and the Coast Guard serving in a combat zone.

Defines "period of lapsed appropriations" as any period during which appropriations are not available due to the absence of the timely enactment of any Act or joint resolution (whether a general appropriations Act or an Act or joint resolution making continuing appropriations) appropriating funds for the payment of the pay and allowances of members of the Armed Forces or civilian employees of the DOD and Coast Guard.