if the back of a plane breaks off, does stuff go flying out?

I would think so

If the plane is at altitude (above 10.000 feet), anything that is loose will go flying out of the aircraft, including people. A British Airways flight where the cockpit window flew off saw the captain pulled out through the front windscreen mid flight. (BA5390 in 1990). In some films this blowout goes on for ages, but the truth is it only lasts a few seconds. As soon as the pressure inside and outside of the aircraft are the same, things stop flying out through the openings.

well the answer is yes every thing does fall out unless the plane is flying backwards then everything gets pushed inside of the plane up to where the pilot sits in the plane

Yes ... the pressure inside the plane at altitude is much greater than outside, so stuff will get blown out of the plane (vs. sucked out as many would say).

Inertia would tend to keep stuff in place but tubulance caused by the wind flowing over the broken end would cause strong air currents that would suck some stuff out and blow other stuff forward.