I have always appreciated backpacks that have a means for quickly adding additional capacity. I am not talking about adding MOLLE pouches which are often too small to make much of a difference on a pack and take a while to thread on and off. The Eagle Industries AIII had side pouches that attached easily via two buckles on the compression straps. Kifaru uses their Dock and Lock pouches to great effect and most of them require just 4 buckles which makes them easy to attach. I have always wondered why similar types of pouches aren’t more common which is why my interest was piqued when a friend told me about Dunamis Gear.
Dunamis Gear has an entire line of pouches like the ones I describe above. Their pouches attach via G-clips to MOLLE compatible bags so they are easy-on and easy-off. They come in a variety of sizes, opening configurations (side zip, top zip, etc.), and other custom options are available.
They can even be useful as standalone bags when you add optional features like handles and shoulder straps. This can be handy for those need to hike in with a large bag but then like to drop their pack at camp while they explore/hunt.