Changing Items Age with /entitydata gives you an extra item when using /give.

When giving you self an item and the command bellow (The "Age" can be set to any value) is running on an always active repeating command block, it will give you one extra of the item your giving youself when using when using the give command.

The Command : /entitydata @e[type=Item] {Age:100}

Example : I use /give @a spawn_egg 3 0
Instead of the game giving me 3 spawn eggs it gives me 4.