The Booster Pack is a rare piece of equipment in Star Fox: Assault that allows its wearer to hover using Gravity Diffusion, the same hovering technology used for the Arwing and the Landmaster. On the Star Fox Assault website, information says that the Booster Pack is one of Fox's favorites. You can unlock the Booster Pack in VS. Mode by playing 90 sucessful matches.
The Booster Pack is activated via the jump button. Pressing and holding it enables the one equipped with the pack to hover. It is useful in that the player can reach places otherwise impossible to go to.