Heading into the Research Room, players can find a Mexalixir, an armor piece called Escort Guard, the ultimate weapon for Yuffie named Conformer, and the powerful Double Cut Materia, which allows a character to attack twice when executing his or her turn, and at higher levels allows the character to hit four times as opposed to twice.
If the player goes into the Hallway prior to events in Midgar at the end of disk two, the party will be greeted by two Shinra Turks, Reno and Rude, waiting to ambush Cloud and the gang. Other than the fight, nothing else can be found in that room. However, the hallway leads to the large open Cargo Room which is where most of the treasure is contained.
The Cargo Room of The Sunken Gelnika appears to be messy, with a broken down helicopter and barrels scattered about, but certain things that are useful to the player were left intact. There is a chest containing yet another Megalixir, and another chest containing Spirit Lance, a weapon for Cid. Then, between the wrecked helicopter and some other debris, the Hades summon Materia can be found, which is used to summon the powerful Hades to devastate enemies. One can also find the Highwind manual, which is used to teach Cid his final Limit Break move, and finally another chest containing the Outsider weapon, a gun for Vincent to use, can be found in this room.
Overall, The Sunken Gelnika is a treasure trove with many valuable secrets to be found. Not only does it contain the ultimate weapon for one character, it also holds powerful weapons for three other party members, a character's ultimate Limit Break, and a few precious Materia that would definitely help anyone on their way to complete the game.