Instructions
Navigate to the Minecraft Workbench website click "Download." When the download is complete, right-click on the file and select "Extract." Double-click the "INVedit" file to start the application.
Start your copy of "Minecraft" and enter the gameworld. Hold down the left mouse button while facing any resource (wood, stone or sand) and your character will "mine" it.
Walk over the "mined" resource for it to be added to your inventory. You can see your inventory on the bottom of the game screen. Press the "Esc" button and then click "Save & quit to title" once you have at least two different resources in your inventory.
Click the "Open From Game" icon at the top of the screen in "INVedit" and then select the Minecraft "save game" for the world you are playing. You'll find the Minecraft saves in the "saves" folder under the Minecraft folder located under your username in "Users."
Left-click on the resource shown on the right-hand side of the screen in "INVedit" and, while holding down the button, drag the cursor to the inventory slots at the bottom of the application screen. The two resources you mined in the game should display in the inventory -- letting you know that you are editing the right file.
Click on the resource icon in the inventory section of "INVedit" and enter "255" next to "Count" at the top of the application screen. Do this for every resource in the inventory and then click the "Save to Game" button at the top of the screen.
Return to the game and load the world you are playing in. You'll notice that you now have an inventory full of resources to play with. When you run out of resources and don't want to mine it yourself, save the game and use the "INVedit" application to generate more.