Choosing a Vest
A vest or some kind of pouch or pack is required to fly fish. I have always used a vest personally but I have many friends that use a back pack type pouch. It is all personal preference. I will focus on a choosing a vest since that is what I have used for many years:
Features to look for in a vest:
Light weight — you do not need them to be heavy. Once you pack your vest it will add a good amount of weight.
Length — do not get a vest that goes much past your upper torso. If your vest is too long, while you are wading, all your pockets will get wet. Keep it short rather than long.
Size — Do not get a vest that is too tight on you. You will want to wear a vest that you can wear over clothing like a warm shirt / few layers of sweaters / etc. Vests are sized Sm / Med / Lg / X-Lg and so on. Make sure you allow for additional clothes.
Plenty of pockets — you want to be able to carry a number of items and you need the pockets to do so.
Color - you will notice that they are natural or maybe blue for women. You just do not want a bright orange type to scare the fish as you approach the stream. They can see you, you know. You must try and blend in to the natural surroundings as much as possible.
Hands-free loop and Velcro strip — this will allow for you to place your rod in the loop and strap the butt to allow for hands-free feature on the stream. This used to be common but some vests have dropped this feature. It is very nice to have this feature.
Here is a video to show this feature https://www.youtube.com/watch?v=1CStrUOsmnM