There is an Easy Method in StartingInventory:
1. Start a new world in Creative mode.
2. Using the Creative Inventory (or NEI) add the items you want to start new worlds with to your player’s inventory (only the 36 main inventory slots are supported, armor slots are ignored).
3. Once you have populated your inventory with the items you want, close your inventory and execute this command: /startinginv save
4. You will receive a message confirming that your current items have been saved to the config file.
5. To test that your file is saved correctly, clear your inventory and execute this command: /startinginv load
6. The items you saved using /startinginv save will be placed in your inventory.Go to developer website...