INVedit

INVedit is the (more like "some kind of") successor of NBTedit. With it you can create your own porta- wait, wrong game. You can use it to edit your inventory both Singleplayer and Multiplayer, if you're the server admin.

Here's some screeny of a regular game inventory opened in INVedit:




Here's a list of features:
• Loads blocks from the enclosed files (items.txt and the .pngs).
• Groups for faster access of individual blocks.
• Search box lets you filter items.
• If possible, displays item damage as bar.
• Stacks items almost like in the game itself.
• Tabs for editing multiple inventories simultaneously.
• Moving items from one tab to another is possible.
• Quick load and save.

.NET 3.5 is required (Windows). May also work with Mono or Wine (Linux + Mac).
If you're an unexperienced Mac or Ubuntu user, this is probably not the right tool for you.

How to use INVedit -
Close Minecraft.
Open INVedit, go to the second tab/folder and click the drop down arrow.
Open the World you want to edit. You should see your minecraft inventory on the world you chose now.
Now, on the right side you will see a list of items (stone,grass and nearly every item in the game) drag the item on your inventory and set the amount of it you want to have. After you chose the items you want to have in your inventory, double click the third tab on top and save it too
C:\Users\Administrator\AppData\Roaming\.minecraft\ saves\World1\level
Click save and yes. PM/Add me if you need help.

Credits : Copyboy