You don’t need to advertise to the world which brand and model you own via your camera strap. A plain generic strap is a safer option. Pacsafe Strapsafe100 is easily removable with locking carabiners, but can’t be cut by thieves.
Extra Memory Cards
I recommend SanDisk as a solid reliable brand. You don’t have to buy the most expensive card if your camera is not shooting 4K or rapid bursts. Use the widget on the SanDisk website to see which card they recommend for your camera.
Small, light, cheap. Throw it in your backpack and it may just save the day when you haven’t packed your big tripod. (You can also use it to mount your off camera flash.) The Gorillapod is a design classic.
Unless your shooting with an all mechanical film camera, you’re going to be using battery power. Get a spare so you don’t run out of juice.
The world looks better when it’s polarized. Less glare, bluer skies, greener vegetation. Get a pair of polarized sunglasses for your eyes, and a polarized filter for your camera lens. The size of polarizing filter you need will depend on the diameter of the lens. You can find this by checking the back of the lens cap.
Blow bits of dust and dirt from the front of your lens rather than smearing them around with your sweaty T-shirt. This one by Giotto’s also looks like a rocket ship, enough said.
Diffuser / Reflector
Harsh sunlight creates unflattering portraits. Soften the light with a diffuser or bounce in fill with a reflector. Lastolite makes a Difflector that does two jobs in one.
On bright days it can difficult to see images on the back of the LCD screen. The Hoodman allows you to check you got the focus and exposure correct before moving on to the next shot.
Save a large plastic bag, and place it in your camera bag. Use it to protect your camera or other gear from rain. Use it to pick up your dog’s poop, or just make the world a better place and collect trash.