You can make lots of items just by having the w-item materia! All you need is 1 or 2 of the thing you want. To create up to 99 items, all you have to do is this:
First equip the w-item on someone, then go into battle (you may want to get into a low level fight cause this can take a while). Select w-item. Find the item you want on your list, and select it once, then select again so the curser is back on the list. Select the same item again, but don't press ok when the curser is on one of the players or enemies. Press cancel, and you'll notice your stock of that item has risen one. You can continue doing this, just select the item the second time (ok, cancel, ok, cancel...) over and over and you'll stock up!
If you only have one of the thing you want, then select it once, and it'll disapear. Go to any other item and select it, and continue going ok cancel ok cancel and the item you first chose will rise in number!
In Wutai there's a place who will give you free items simply for viewing posters that they have set up around the world. Just for spoting these, they will give you: a megalixir, power source, speed source, luck source, magic source, guard source, and a mind source. It's not much, but it's not bad. Here are the locations of each flyer:
1. In sector 5, on the second floor of a house near the way to Aeris' house. There will be a sick boy on this floor.
2. The first floor of Shinra Tower. In the back near the elevators is a bulletin board, and you'll find it there.
3. In the Gold Saucer's Ghost Hotel, just beside the entrance to the item shop.
4. In Cosmo Canyon, a paper right beside the Weapon's dealer.
5. Another one is in Cosmo Canyon, in the Inn just up the stairs.
6. And the last one is right in Wutai. When you're chasing Yuffie around the place, she finally traps you in the basement of some house. You'll find the poster on that floor near the stairs.
The Gelnika is a great little plane, sunk to the bottom of the ocean. You can reach the Gelnika using your submarine, and can find all sorts of goodies down there. It's location is near Gold Saucer, inside that little inlet there. The fights are pretty tough so if you're not strong enough you'd better prepare. Here's a basic layout of the Gelnika's item stash.
Just inside, there's no fights, just a save point and a good weapon for Cloud called heaven's cloud.
If you enter the door to the back you'll find a megalixir, 2x-cut materia, Yuffie's ultimate weapon and a status guard (great armor for just guys). And the door to the side leads to a fight with Rude and Reno if you haven't already fought them again in Midgar. They have good items on them to steal.
The next room contains a weapon for Cid, Hades materia, another megalixir, Cid's ultimate limit break (Highwind), and one other thing...I forgot.
This is a place you shouldn't miss. It's the perfect place to return and fight if you want to increase your level.
Yuffie - You can only aquire Yuffie if you encounter her in a battle. You can find her in any forest at anytime, defeat her and she's in your party. But after you defeat her you have to say the right things or else she'll run away. First thing, don't use the save point you see. Anytime you go into your menu she'll just be gone, and you've lost her forever. Here's what you need to say:
First she'll ask if you want to fight again. Say no.
Then, she'll ask if you're afraid of her. Tell her you're TERRIFIED!! Which I'm sure you are.
Then she'll say you're implying that you want her to join you. Say yes.
Lastly, do not ask her her name, just say lets go and she'll tell you her name later. Like I say, you can't let her out of your sight for a minute.
Vincent - In the Shinra Mansion, he's in the basement, locked up and going insane. He's such a weenie. Anyway, you first have to open a safe using a code, which numbers you can find around the mansion. But to make it short, here's the code:
Right 36
Left 10
Right 59
Right 97
At the beginnng of disk three, you'll see a big weapon floating over a crater near Junon. This guy is worth fighting, from him you get Cloud's ultimate weapon and you can get into a place called the hidden forest. To fight him, simply run into him with your airship. After you damage him alot, he'll fly away, and your back on the highwind again. And where did weapon go??? He's flying away from you, you scary guy! Stay up with him for as long as you can. But he'll keep on flying around if you don't hit him quite a bit with the highwind. After a few hits, he'll go straight to another place and land. Now, you can save and rest or whatever and do the whole thing over again. This will happen maybe about 5 times, until he finally ends up near cosmo canyon for the final fight. Defeat him and get Cloud's weapon, and his blast will lead the way to the hidden forest.
After defeating ultimate weapon, you can get to this confusing rainforest type place. Inside you'll find bugs, frogs, flowers, and all sorts of things to help you get along. Try using them for different things, pick them up, put them in flowers, use beehives, just mess around. It's not so hard, and there's plenty of good treasure. :) I'm not going to tell you every single move to make because it's fun to try it all on your own. Really. I'm not trying to be cheap. It's cool to discover it all on your own. Try it!! If you don't like it, you can always leave. So don't worry. :)