Tripods (February 2018)
You can accomplish maximum stability for your spotting scope, or camera setup by using a heavy, wooden tripod, with spiked feet, without a center column, and with a heavy head. But note that you might end up leaving the heavy tripod at home if you plan to move around a lot.
Instead I would compromise a bit and use a medium size tripod that also can be stowed into my check-in luggage. The one thing I would not settle on is Carbon Fiber. This material is sturdy and comfortable to touch in both hot and cold weather.
I would go with a 2-way Fluid Video Head. After many years of using different tripod heads I have always come back to the Manfrotto heads. They are very priceworthy and best in class. The smooth pan of these types of heads are perfect for spottingscope users following a bird, or videographers.
The standard for supporting super telephoto lenses on tripods, replacing the video fluid head as they would tip over with all that weight. The most famous Gimbal Heads is the Wimberley heads. They enable amazing maneuverability for huge lenses, and have been recommended by the best. The closest competitors are Sirui Gimbal PH-20 followed by Induro GHB2.
I rarely use monopods, but they are useful in offloading your shoulders when using heavy lenses. But in most circumstances a tripod is to be preferred. Manfrotto/Bogen 681B ($50) is a large sized aluminum monopod that is extremely sturdy. I own a Velbon CF-7 ($130) which is a slightly smaller Carbon Fiber monopod with antirotation twist leg locks, and a useful shoulder carrying strap. Both monopods are insulated at the top of the monopod, and the leg locks only need one hand to resize the monopod. I also have a monopod in my Benro Travel Angel tripod, just twist off one of the legs and extend with the center column.
Skimmer Ground Pod
When getting low on muddy and sandy soil then a tripod can be awkward to move about. Naturescapes Skimmer Ground Pod II ($100) is the best product for this type of terrain. You can also create your own with a frisbee and a beanbag. The key is to get low when photographing shorebirds especially.
I have had a BlackRapid shoulder strap since 2011 and it has made it much easier walking around with my 100-400 lens, not worrying about it sliding off the shoulder. But as a precaution check both the camera fastener and the connector on the strap before heading out. I have seen the old connector break after extensive use, and the camera + lens crash onto the ground. The new connector with its cover seems to be a better design so do not let that discourage the use. Just replace it before the metal wears out.
These have long been custom made contraptions. I was lucky to buy a very good model from the former Bushhawk company. I wish it could resurrect and make adapters to my different Canon cameras. I liked it especially when photographing from a boat.
Backpacks & Belts
I have used a Lowe Photo Backpack for years. I have put it into my carry-on with wheels when travelling so that I can pull it along instead. When I arrive to where I will be staying I simply unzip it and lift out my camera backpack, ready to go. But sometimes I use a waterproof bag instead. The only concern there is that I need to carefully pad the equipment against drops or dings that can happen when putting down the bag. I will use this waterproof bag on backpacking trips, or when I need every little space possible.
I have recently purchased from thinkTank a padded belt and a camera pouch that I can attach to it. I hope it will be better for when hiking, or maneuvering in difficult terrain. Not to mention the less strain it will be on my shoulders compared to straps and backpacks.