A popular product at our store, the Patagonia Front Vest Sling offers the functionality of a sling pack plus the a front "mini vest" for easy access to your most used tools and accessories.
The front portion of the Front Vest Sling has three exterior and two interior pockets plus areas to attach tools, such as forceps, line clippers, etc. The main compartment of the pack has multiple pockets for additional fly boxes, a rain jacket, and other items. Additionally, the Front Vest Sling has a water bottle holder, a d-ring to attach a net, and many other features that make it a super cool pack for a day on the river.
For quick access to the main compartment, simply detach a clip and rotate the pack under your left arm. There is no need to take the pack off as is the case with traditional backpack designs.