The Rocket power-up clears the vertical line of blocks. It also clears one layer of blockers. The exceptions are:

 - Locks

 - Hives (if there's honey around it)

 - Candles (rocket can light them up, but not remove them)

 - Boxing bags (rocket hits them once but doesn't remove them)

 - Closed oysters

 - Bowling balls and pins

To use the Rocket, tap the Rocket button and then tap the column you wish to clear.