Simply put, in many videos I see people in the holding area rushing to pick up the guns in the holding area just to spray the bullets in the face of their friends. However, I was wondering if they keep their guns when they are put on the plane?
As Kevin mentioned, it is just for the fun of it, and for brand new players it's an area to get a quick chance to play around with the controls, movement and a feel for the weapons.
Although in contradiction to what Kevin said, "Each player starts with the same gear" - there is no gear at all at the start. Every person enters the plane with nothing on them other than the aesthetic clothing they equip (or not equip, yes you can play with just your underwear).
In addition to the comment about dropped gear not coming onto the plane, you can also drop your gear while on the plane, but where it goes I have no idea.