Jack beat me to it. Also, since most bags will have multiple pockets you can keep a spare change of clothes, baby wipes, deodorant, and breath mints handy. Breath mints especially for a biter, 'cause, 'ew.
But yeah, for 'shifters or mages using the shapeshift spell that bag solves a lot of stupid little logistical problems.
Tack on Gear Access for extra lulz.