This 7.5 liter fully waterproof (IPX-7 rated) fly fishing sling pack with easy to use airtight zippers is large enough to carry your fishing gear for the day and probably a lunch as well. It is also small enough that you don't feel like you have a large backpack on one shoulder. It has comfortable and breathable padding for your back and shoulder so you can wear it all day.
Specs for the NIRVANA Waterproof Fly Fishing Sling:
Weight: 1.24 lbs (20 ounces)
Compartment size: 8.7" wide x 14.6" tall x 4.3" deep
