Besides my camera body, and whatever lenses I am traveling with for the assignment I plan to be shooting, I always carry the following 10 items in my camera bag:

1 – An Extra Camera Mounting Plate For My Tripod.
There have been times where I have removed the tripod mounting plate from my camera after a shoot and then forgotten to reattach it to my tripod. Then when I went out on my next shoot I had no means of attaching my camera to my tripod. So keeping an extra backup tripod plate in your camera bag means you always have a spare mounting plate with you if you pull out your tripod and find that the camera mounting plate is missing from it.

2 – Remote Shutter Release. Almost all cameras have self-timers for hands-free operation of the shutter release, but it is not always convenient to wait 5 or 10 seconds for the self-timer to fire every time you want to release the shutter remotely. A remote cable release allows you to trigger your camera’s shutter at the precise moment that you want, but without needing to physically touch the shutter button and risk creating vibration to the camera. Also, cable releases will allow you to stand off a short distance to the side of the camera so that you can trigger the camera’s shutter in low light and long exposure situations also without touching the camera itself.

3 – Light Meter. A light meter is always good to have in your bag. Normally you can get away these days with using the image preview screen and the histogram on your DSLR camera to figure out what your exposure should be in tricky lighting situations, but it never hurts to have one just in case you want to meter for the true correct exposure level for a difficult lighting situation.

4 – Extra Battery And Battery Charger. Even though most DSLR cameras have very good battery life now, it never hurts to have a backup battery. There will be times where you might be using your preview screen a lot and/or shooting with live view and running down your battery faster than expected. Also, if you are shooting tethered, this consumes extra battery power from the camera to transfer pictures via the camera’s USB cable to a tethered device. A second fully charged battery in your bag is an indispensible thing to have. Also, if your battery charger is small it is good to bring it along too because if one battery does wear down completely then you can swap to the backup battery, continue shooting, but then also start charging the worn down battery at the same time. This way you always have a fully charged backup battery at all times.

5 – Polarizing Filter. There isn’t much need for filters anymore these days when shooting with DSLR cameras because of the ability to mimic most filter effects now during post processing, but a polarizing filter to remove glare and reflections on water and glass can always be useful to have in your bag. Also, reflections and glare in post processing can be very difficult to remove. So a polarizing filter is almost necessary in some cases. I actually have a few different sized polarizing filters in my bag as the front diameter of my lenses vary and some lenses require different sized filters.

6 – Microfiber Cloth & Dust Blower. It is always good to have these items in your bag as you never know when you are going to get some dirt or dust on your lens and/or your sensor which might need to be cleaned off when you are out shooting.

7 – Extra Memory Cards & Card Reader. It is always good to carry extra memory cards. Memory cards get full, sometimes they even fail and you need to change them out, so it is good to be prepared with extras even if your main memory card has a large storage capacity already. I also always carry a memory card reader as well since you never know when you may want to download some of your pictures onto a computer on the fly.

8 – Extra Studio Flash Fuses. Since I am often shooting on location with my studio flashes I carry extra fuses for the flashes. Most studio flashes have fuses as a safety precaution when there are power surges. If a fuse blows and you don’t have extra ones with you then you could find your studio flashes useless on a shoot. So it is always good to have some extra fuses in your camera bag just in case.

9 – Spirit Level. A spirit level which fits into your camera’s hot shoe is an invaluable tool for leveling your camera on your tripod when shooting any sort of architecture or landscapes. I never go anywhere without one or two in my bag.

10 – Wireless Flash Trigger. Again, since I am often traveling with studio flashes I always carry a couple of wireless radio triggers so that I can remotely trigger and sync my camera with my studio flashes on location. I use radio as opposed to infrared triggers since infrared triggers often wont work outdoors in strong daylight.

If you feel there are any other must have items in your camera bag which I forgot to mention here then please feel free to post them below.