Which parts of an airplane are made of buoyant material?
Passengers are reminded of #1 &amp; 2 above on every safety brief.
Beyond that, you aren't going to get up out of your seat before the crash and attempt to latch on to some buoyant part of the structure, so it isn't an actionable question in the context it is asked.  (Which is a polite way of saying who cares...)
Stay in your seat until the violent motion stops, then follow the instructions of the surviving crew to evacuate the aircraft in an orderly manner.
Allow women and children to go first if able.  Whatever might be floating after the crash is over is buoyant, and may be used.