You do not need any items. All you need is a very hard luck. The ID number of the first Pokémon in your party should match with the floating point number of the mirage island. If it matches, talk to the man in Pacifidlog. You can now travel to mirage island.
Sadly, the only thing you can catch at Mirage Island is Wynuat, but you can find lots of rare Berries and Items there.
You can only breed pokemon, not items. Items aren't alive!
dont care
A Razor Fang can be found on Mirage Island and Cresent Isle, which a Item Finder is required to find these items.
there are a few items , but the Pokemon SMEARGLE is inside
You can't duplicate items unless you use a gameshark
you can't get jirachi in emerald, only by Nintendo events, they give out special items that helps you get rare Pokemon.
YES, duplicating Pokemon and items, going to moon etc
click on the pokeball in front of you and it should be an item
Some of them contain items.
As far as I know there is no code for key items.
Google: How to clone pokemon in pokemon emerald. Be warned, this may ruin the fun for you, and it does work. Be very very careful. Think of it as a last resort, once you have had all the fun you can in emerald, then use this cheat.