Lightest-Bean Bag
The lightest option is some sort of small bean bag. You can easily make these yourself to fit your camera size. A soft hacky-sack will work for some cameras in a pinch. These provide some cushion and cradle on surfaces, such as a rock or the crook of a tree, commonly found while out hiking.
Light Tripods
For small point-and-shoot cameras, tiny tripods are available that have wiry telescopic legs and won't come off the ground much more than a foot. Small tripods with knobby, articulated legs allow you to attach the tripod to a tree branch or balance on a rock or other uneven surface.
Medium Tripods
If you carry a bigger camera such as an SLR, you'll need a more substantial tripod to keep the camera steady and balanced. Larger models of the knobby, articulated tripods work well with these cameras and are the lightest option.
Full Tripods
For more involved photography, such as precise landscape photography or even for wildlife, carry a big tripod along with those big heavy lenses. A heavier tripod helps to keep it steady, but many full-length tripods are available in carbon fiber to minimize weight. You can clip your backpack under the tripod to make use of weight you already have with you. Some tripods come with a sling where you can add rocks or other sorts of weights for stability.
Monopods
Monopods are popular to simply steady the camera to frame the shot. They often double as walking sticks (though don't leave the camera attached when using the monopod as a walking stick). Monopods are not a good option if you're looking to do any sort of night or time-lapse photography and need to set the camera to take long exposures. They also don't work well for time-delay shots to get the photographer in the photo with the group.
