The Star Army Butt Pack is a padded sack primarily designed to attach at the waist to power armors like the Ke-M2 "Mindy" Series of Power Armor. It contains a large central compartment (with a hanging pouch) and two cushioned side pockets, along with a flat rear zippered compartment. The butt pack need not be used on power armor; it can also be easily attached to soldiers' load-bearing vests. The pack is also extremely heat and radiation-resistant as to survive the radiation created by aether sabers and teleportation. It was first used in YE 29.

Packs are available from Ketsurui Zaibatsu in black, dark gray, Star Army Cadet Blue, white (from YE 45) and RIKUPAT (from YE 37 onward). Some older butt packs may have the "Multi-Net" Camouflage Pattern. Butt packs are always issued with a matching waterproof bag. While the butt pack itself has a water resistant coating, it is not waterproof and won't keep water out if submerged.

Typically, the butt pack is used to carry a Type 31A Survival Kit or a Type 31C Medical Kit, along with a spare uniform or Environmental Suit.