When shooting outdoors, especially on long photo shoots, you'll often need comfortable clothes that protect you and your camera from temperature changes and bad weather.
Equally as important, they need to feature plenty of pockets in order for you to be able to store essential accessories. That's why a photographer-friendly vest or jacket is useful.
The exact features you need will largely depend upon your individual style of shooting and photographic genre. Nevertheless, here are the key features to look out for when choosing a photography jacket or vest:
Make sure you try before you buy wherever possible, or if you're buying online pay close attention to the manufacturer's sizing guidelines. Also look out for features such as draw cords at the waist/hem, adjustable sleeves and so on, since these all help you to tailor the garment to your shape for the highest level of comfort.
Windproof fabric, taped seams, waterproofing treatments such as Nikwax and Teflon coatings, generous flaps to protect pockets and well-proportioned hoods with visors are all desirable when it comes to keeping yourself protected from the elements.
If you're a cold-weather photographer, you could consider a specialised winter garment rather than an all-season jacket, or opt for a lightweight version that you can use as part of a layering system.
Breathable fabrics and built-in vents around the back and under the arms will enable moisture to escape, helping you to stay dry and comfortable.
Check that the jacket offers enough pockets for your individual needs, and that the method of fastening them suits your photographic genre (ie avoid Velcro if you need to stay quiet while shooting).