Your question is not a one size fits all type. One guy like blonds the other red heads. I think you get my point. I will buy synthetic materials on line with out seeing them. However natural materials such as hair and hackle is better purchased by looking at it before buying it. There is big different in hackle for different applications. Quality dry fly hackle to make dry flys is stiff, repels water and comes from rosters.Necks can cost a few dollars to over a hundred. Tails from deer or calf's can have long hair or short hair (not long enough depending on what you are tying). Also most calf(kip) tails have some black hair at the base of it. If you can use the short black hair great if not look for one that has the least amount of waste. Also some hair will be hollow. Especially deer body hair. This is to keep the animal warm and repel rain. However it flairs when used and will be a problem for new tyers trying to use it on jig or streamer patterns. Going to a fly shop or at least talking to the shop owner can be a big help especially for beginner tyers! A good starting tip is go to your local craft store or Walmart and get some synthetic fur. It is cheap and in many colors. Liftbite is giving some very good advice.