They are available from many of the companies listed, and they have a range of features such as removable shoulder straps, belt loops, and accessory pockets. Compact, light, easy to carry, surprisingly good protection. Small, light, surprisingly good protection. There is a wide choice here. Most are designed very carefully to give the best protection to your camera gear, and also to protect against back strain from poorly loaded, ill-fitting frames.
Companies keep working on their designs and the bags keep getting better and better.
Tamrac had rolling backpacks, Lowepro has modular backpacks. The easiest way to carry a heavy kit any distance, or any kit for long distances. Secure, good protection. I have already indicated that I use these a lot. They are not as common as full-size packs, but they are increasingly popular.