Which parts of an airplane are made of buoyant material? Which parts of an airplane (to make this question more specific: accessible in the main fuselage where the passengers are aboard) are made of buoyant material.
Imagine a plane is about to crash into the sea, you might wanna hang on to something that could keep you afloat, so here’s a few things that I think are buoyant(based on the floating debris seen after a crash):

The life vest/jackets which we can inflate
Seats
The doors(the ones through which we enter or any other door)

Which things would someone want to hold onto, to increase chances of survival?
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.