"Midrats" is a Navy term for "midnight rations". This is a meal in addition to breakfast, lunch, and dinner, and is generally dinner left-overs, breakfast items, and easy to fix items (hot dogs/sandwiches). It is served primarily for sailors and Marines working late night shifts or watches.
It is not unusual for Navy SEAL's to hitch a ride on support vessels like the USS Keating, however they do not usually deploy from support vessels for extended combat missions. The Keating is a San Antonio-class amphibious transport dock, which is primarily used to transport and deploy amphibious assault vehicles; the ship has no offensive capabilities and is only armed with two Bushmaster 30mm close-in guns, three twin Browning M2 anti-aircraft machine gun turrets and a Rolling Airframe Missile launcher for defense against anti-ship missiles, it does not have the ability to provide fire support if needed. Which is why for this type of mission SEAL teams usually deploy from either a Ticonderoga-class guided missile cruiser or an Arleigh Burke-class guided missile destroyer, which can provide both air and fire support.