The Best:
I have three to list that I bought in bulk on the cheap, cheap and now they are either discontinued or too expensive to buy in the quantities I did so I feel like a genius.
Gudebrod Fly Tying Thread - In a ton of colors in 3/0 through 10/0. It is my hands down favorite thread and all I've used for a LONG time. I stocked up on the cheap after they went bankrupt.
Whiting 100 Packs - From size 12 down in a bunch of sizes and colors you can't even get anymore. I literally have hundreds of 100's packs. I was snapping them up at $6.00 - $8.00 before the hair craze so I am set forever with dry fly hackle.
Frank Matarelli Bobbins & Tools - The first bobbin & whip finisher I ever bought were Matarelli and they have been with me ever since. Around 10 or more years ago I added a BUNCH to my collection, especially the bobbins (long tube, regular & midge) since I like to keep more than few loaded with thread so I don't have to swap spools. Frank is gone and the company is out of business.
Have you seen what real Matarelli stuff goes for on eBay?
The Worst:
Pettijean Magic Tool Set - I bought this set after seeing it demonstrated someplace. The only magic thing about it was how it made my money disappear. The only good news is I didn't pay anywhere near what they get for them now.
BTW - I've never used it...
The ???:
Toenail Clippers - I tie & fish a lot of foam beetles. My process involves first pre-cutting diamond shaped pieces of flat foam. I tie in the foam by one diamond "point," build my body and pull the foam over and tie it off at the other diamond "point."
I have this pair of toenail clippers I got somewhere about a 1000 years ago with the PERFECT curvature to clip the points on the sides of the foam to give it that PERFECT beetle shape. Most other toenail clippers I've seen have a much shallower curve and would require more clipping to get the same result so I guard this pair with my life!