midstream,

That's a dangerous question! I understand your frustration though. When you want to tie a new fly and there is just one item that you're missing, it's very discouraging. But I don't think you should just buy stuff based on people's suggestions. There are thousands of fly patterns and we all have different tastes.

What I do is keep a small notepad at my tying bench. When I want to tie a new pattern that I'm missing materials for, I just write it down in my pad and keep a running "grocery list". The next time I'm ready to do a catalog order, I just check my pad and see what I need. Of course if I just need an item that I think I can get at my local fly shop, I'll just run out and get it.