Shoulder straps double as either a sling or backpack style with one pull oo the zipper. The top zipper opens up to a generous extra storage area for say hats and gloves, etc. Pulling down the main zipper from front to back expands the main storage bag storage area. 

Inside, the zipper pocket opens up to a storage area of about 6 1/2" x 4-1/2". Outside, thera are two large storage pockets on each side that measure about 6" x 6-1/2" x 1-/3/4".