Compression Straps
This is really a feature found most often on IF packs. Compression straps basically allow you to compress the size of the pack around the loaded equipment to provide a tight and stable "package". If you're carrying gear on a hot summer weekend, you might not carry as much as you would on a late autumn trip. You may not have enough equipment inside to fill the pack to its full dimensions. Compression straps close up this extra space. They're most often located on the sides of the pack - a simple strap and buckle arrangement. Some IF packs with a single compression strap on each side, or as many as three. Some packs may have compression straps that run over the back of the pack as well or even straps that pull vertical rods for even compression. Same theory, different variation.

Sleeping Bag Compression Straps
A few IF pack manufacturers also include vertical compression straps and buckles that run over the sleeping bag compartment. These straps can be connected when the sleeping bag is stuffed half-way into the sleeping bag compartment and tightened down to compress the remaining part of the sleeping bag, making it easier to stuff. Nice feature, especially if you're trying to get a large winter synthetic sleeping bag into the compartment. The straps can also serve double duty by providing another means of carrying a tent or sleeping pad securely on the outside of the pack.

Sternum Straps
Most larger packs may have an additional adjustable buckle and strap arrangement that connects the shoulder straps together. The sternum strap is designed to distribute weight across the front of the chest. This can relieve pressure at the front of the shoulders and generally make the pack marginally more comfortable to carry under load. Sternum straps also pull the straps closer to the center of the body, allow increased arm flexibility and range of motion, and prevent straps from slipping off the shoulder when leaning over or scrambling over rough terrain.

"Articulated" Straps
Better pack designs will also fashion shoulder straps to more naturally follow the contours of the body. "Articulated" shoulder straps generally have a built-in curvature that follows the natural route of the strap over the shoulder and down the side of the body. Obviously, this design is more comfortable than a strap that is simply a straight piece of nylon covered foam. On packs designed for women, shoulder straps are also sometimes designed to allow for natural body curvature at the bust.

Load Stabilization Straps
Found almost exclusively on IF packs, load stabilization straps are supplementary straps that run from the top of the shoulder strap up to an attachment point on the pack around ear level. These supplementary straps allow you to adjust the distance between your back and your pack. On uphill pulls were it's advantageous to have the weight close to your back, these straps can be tightened to pull the top of the pack close to your body. On downhill strolls, the straps can be loosened to move the center of gravity more towards the middle of your body and the pack. Some also like this feature during the summer, when the straps can be loosened to provide some ventilation between the back and the pack. Some pack designs might also include lower load stabilization straps from the area of the sleeping bag compartment to the hip belt. These straps are designed to minimize pack "swaying" at the bottom of the pack.