Final Fantasy VII/Things to Collect

Materia caves

 * HP <-> MP: Found in the cave north of North Corel (the ropeway station).  You must have a black Chocobo to reach it.
 * Quadra Magic: Found on an island to the east of Chocobo Billy's Farm.  You must have a river Chocobo to reach it.
 * Mime: Found on Wutai Island, on the eastern edge south of Wutai's northern peninsula.  You must have a mountain Chocobo to reach it.
 * Knights of Round: Found on Circle Island, an uncharted island in the northeast part of the world map.  You must have a gold Chocobo to reach it.

Turtle's Paradise flyers
Throughout the game, you will find posters that advertise Turtle's Paradise, the restaurant in Wutai. After viewing all the Turtle's Paradise flyers, you have to read the main poster in front of the Turtle's Paradise bar in Wutai. If you found them all, you can collect the prize from the barkeeper in Turtle's Paradise.
 * Sector 5 slums: In the top floor of one of the houses.
 * Shinra headquarters: First floor on the bulletin board. You have to read this on either time you're visiting the building, or you'll miss it for good.
 * Gold Saucer: Ghost Square shop.
 * Cosmo Canyon: Weapon shop.
 * Cosmo Canyon: Shildra Inn.
 * Wutai: In Yuffie's House in the cellar.

Ribbons
Ribbons are a very handy accessory, as they block all status effects. They're also pretty rare, but here are some places to get them:
 * A chest in Temple of the Ancients.
 * Master Tonberrys can be morphed into extra Ribbons.
 * There's a pretty well-hidden cave in Gaea's Cliff.
 * Complete the Special Battle in Gold Saucer ten times
 * Morph Ho-Chu, the 2nd opponent in Battle Arena Special Battle & a random final opponent in Regular Battle

Bone Village
The Key to Sector 5 can be found by looking for normal treasure. If the tremors point toward the fighter plane's nose on the lower plateau, dig just under the tip to reveal it. This is the most probable location for it, though it may vary.

Lucrecia's Waterfall
You need a green, black, or gold Chocobo or a submarine to reach the round lake on the southern half of the western continent. There's a cave behind the waterfall. Once you enter with Vincent in your party on Disc 2, you get a cutscene that explains a lot about Vincent's background.

Return to the cave after about one hour or more of play time in Disc 3. Doing so, you'll get Vincent's level 4 limit break manual Chaos, and Vincent's ultimate weapon Death Penalty.

Sunken Gelnika
A big airplane has sunk southwest of Costa del Sol. Use the submarine to reach it. Be careful about Emerald Weapon though. If you spot it and can't escape, press and you will emerge from the water.

Inside, there's first a save point and a chest. In the second room to the left, not up the ladder, you have to fight Rude and Reno of the Turks. Rude does Bolt2, and both Reno and Rude both have admirable physical attacks that will amp your limit bars. Be careful of their confuse though. Two good strategies here are to equip Steal materia and steal the most valuable and prized armour in the game, Ziedrich from Rude, and also Touph Ring from Reno, and to use Hypers on your party to quicken their wait time and fill their limit bars faster. This is one of three chances to steal the Ziedrich armour from Rude. The other spots are at the Rocket launch site and during Return to Midgar.

The third room is the cargo room. Behind the pipes, you'll find Hades materia. In the top-right corner, there's a Double Cut materia hidden from view by one of the chests on a higher catwalk. In the chests, you find Conformer, Yuffie's ultimate weapon, Highwind, Cid's level 4 limit break manual, along with other items.

The enemies here are very strong, from around a few hundred to two thousand damage, but they can be morphed into Sources, which raise your stats. Getting Sources here is the only way to raise stats to the max value of 255; you cannot reach this point by leveling up.