The Sack Pocket allows the player to use created or given power-ups at will in a level. The creator has to use the setting 'allow Sack Pocket' to let players use the Pocket or not.
The Sack Pocket can be accessed by pressing the O button.
"You can't have too many pockets. This is precisely why I want to introduce you to the all new SACKPOCKET. Press the BACK BUTTON to bring up the SACKPOCKET. Use your LEFT STICK to highlight the particular thing you wish to pull out of the SACKPOCKET and press the ACTION BUTTON to select it. See how it's now in your hands? That's pock-tech for you. How anyone got by before pockets is beyond me..."