From the Super Mario Wiki
A Booster Barrel is a type of Barrel that appears in Donkey Kong Country 3: Dixie Kong's Double Trouble!, Donkey Kong Land III, DK: King of Swing and DK: Jungle Climber. This special barrel allows the members of the Kong Family to reach higher ground. The Booster Barrel looks like a normal Barrel Cannon, except the arrow comes apart in the back to represent speed lines. When the Kongs jump into this wooden device, flames will immediately blast out of the bottom of the barrel like a rocket. The Booster Barrel (with the Kongs inside) will then shoot straight up into the sky until it reaches a predetermined location. While at this spot, the barrel will launch the heroes upwards into the air. The Kongs can then maneuver left or right while in mid-air to land on stable ground. Upon releasing the apes, the Booster Barrel will descend to its original position. Booster Barrels are typically found in waterfall levels, as these stages often require the Kongs to ascend vertically to the top of the waterfalls.