The ornamental design for a portablestoragecontainer, as shown and described.
1. Portable storage container
1.1 : Front
1.2 : Top
1.3 : Bottom
1.4 : Left
1.5 : Back
1.6 : Perspective
1.7 : Perspective
The right side view is omitted because it is a mirror image of the left side view; the parts shown by means of broken lines in the reproductions are not part of the claimed design; the thin parallel lines in the reproductions represent contours only and do not illustrate an ornamentation or decoration of the surface of the product.