Bag of Many Bags

This cloth sack is indistinguishable from any other sack normally found in a market square. However, if a detect magic spell is cast, a faint aura of evocation magic is discovered.

The sack can hold any mundane or magical items placed within it--to the normal capacity of the bag. However, its magical nature cannot be called into play unless it is empty. When placed on the ground and the word "backpack" is spoken, the bag of many bags transforms into a normal canvas backpack. The words "flask," "small sack," "large sack," "belt pouch," "bucket," "vial," and "water skin" have like effects on the bag.

Adapted from Polyhedron Newszine #90.

Image generated with Stable Diffusion.