Just like you wouldn't go swimming with clothes on or eat pizza without sausage (c'mon, you're not a savage), you wouldn't take the ABS Powder Base Unit into avalanche terrain without a Powder Zip-On 15 Cover. Most importantly, the avalanche airbag won't work without the cover, but you also won't be able to carry all the essential avy gear you need: the Zip-On 15 has an easily-accessible pocket for your shovel and probe, and ski and snowboard mounts to let you go hands-free (it's not just for businessmen anymore!) when the skin track turns into a near-vertical bootpack.
To further ease your passage, the Zip-On 15 is compatible with a hydration bladder and has a stowable helmet net so you don't need to leave your brain bucket behind just because you've got some ground to cover. It's also interchangeable with ABS' five-liter cover, so you can fine-tune your pack to suit the day's needs—the 15 is perfect for a day tour, and the 5 for super-minimal light 'n' fast assaults. No matter how much gear you need, you'll have the backup of ABS TwinBag airbag system (a part of the ABS Powder Base Unit), proven to help you stay on the surface of avalanches.