Over the years, I have tried a lot of different accessories to help stabilize my camera when I am not using a tripod, from chains attached to the tripod socket and then you step on the chain to shoulder pods and more. Two accessories I use constantly are a beanbag and a monopod.
I always keep a beanbag in my camera bag. I have an old Steadybag that I have had repaired multiple times over the time I have used it. It is still available, at least over the internet here. It has been a solid performer for me. My beanbag is actually filled with plastic pellets (they don't absorb water like the traditional beans used, plus they are very light).
I use this beanbag a lot for low angle shots when my camera is on the ground or near the ground. You simply put the bag on the ground and settle the camera into it. It then holds the camera in position (not extreme positions) and keeps it steady when you shoot. I have also carried it when I needed to travel really light, without a tripod. I will set the bag on a rock, a fence post, or anything else solid and stable. You can even hold the camera against a vertical support with the bag between the camera and surface.
I also use the beanbag with my tripod to help stabilize the camera without actually attaching the camera to the tripod. This can be more convenient for low angle shots and when you need to move quickly. I have even used a beanbag on top of the tripod when I forgot a quick-release plate on my camera and could not use the tripod otherwise (all of my cameras have quick-release plates that fit into Really Right Stuff quick-release mounts on my tripods).
I used to use a monopod much more in the past than I do today. That is because carbon-fiber tripods are so light that especially with the smaller ones I can use with my Micro Four Thirds cameras, carrying a tripod is much less of a chore. In the days of metal tripods, carrying a monopod made a big difference.
Still, a monopod can help in certain situations. I use mine for some insect photography when I have to keep moving to keep up with the insects. I can set the monopod up and simply lean and pivot it as needed, allowing me to keep the camera in position without the fatigue of trying to constantly hold it up. This can also be a benefit for wildlife photography to help support a camera with telephoto as you work an area for animals. I have also used my monopod as a hiking staff substitute that can also be a sturdy camera support (actual hiking staffs can be used, but they are not as sturdy) when hiking without a tripod. And I have used a monopod while photographing when wading through a swamp.
I actually have two monopods. One is a standard pod with a standard round tip at the base of the leg. The other has a mini-tripod mount attached (I got it from ebay) to give a base that allows the monopod to be tilted around without slipping on the ground or other surface. They also have quick release heads to make it easy to put a camera on and off.