First you need to download two programs: 360Revolution and Horizon.

Here are the links:
360Revolution The link won't work for this so just google 360revolution and download it.

Horizon
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First, make sure your inventory is full and then save.

Second you need to put your save game from Minecraft onto your USB.

Next open your save in Horizon.
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Then extract your save using Horizon to the desktop.



Next, open up 360Revolution and look for the Minecraft Editor.
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Load your save game.



Right click and select Max all items amount.
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Then replace whatever you had in your inventory with whatever you want.

Then, click save, and exit 360Revolution.

Next, open your Minecraft folder in Horizon and right click and click inject file. Inject the file from your desktop and click yes to overwrite and then your done.

Andddd there you go...

I am not responsible if you get banned. Whenever you mod there is always a chance of getting banned. Mod at your own risk.