First, make sure your camera bag is well organized. Know exactly where each piece of gear is located inside the bag so you can access it as quickly as possible. Second, if you know you will want to use a particular camera body and lens combination, have it connected and ready to use inside the camera bag. Finally, think about using a holster style of camera bag, which just holds one camera and lens, keeping the gear within easy grasp at your side or on your chest.