I have more than a few one-off unusual gadgets for fishing and for the most part, I designed and faricated them all or in the case of a few, I had them made for me.
These include a leader dispenser with an attached tippet guage and a battery powered spool motor for refilling that holds 6 spools of tippet material in a plastic box measuring 4.25" x 3.25" x .75", a bench top line winder that loads or reverses any kind of fishing line on any kind of reel, a flashlight holder that attaches to the magnifier on my hat brim that can be pivoted up or down, but especially down into my Richardson Box.
I've also designed & made holders for everything from fly floatant, walkie talkies to soap, modified my Richardson Box so I can swap trays, made a magnetic rod holder with a collapsible pouch that cradles & protects my reel and rod butt while having the ability to swivel 180+ degrees so I can use it to safely string up my rod.
I've also designed and fabricated removable compartmentalized inserts for my Chapman over-the-shoulder fishing bag and designed other Chapman bespoke gear, designed a custom Wood River bag for conventional bass fishing that Peter Ross the owner fabricated for me and I designed and built a removable extension for a collapsible McLean long handled net that makes it a bank or boat angler's dream at 21 inches, 48 inches or 64 inches long.
However my based on when I got it and how extremely UNUSUAL it was at THAT time...
I'd say a zinger tops the list despite me not having a thing to do with the idea.
This is what MY first zinger looked like except they were ONLY known as "retractors" back then:
Orvis offered them WITH & without Old Pal nippers. My first was obtained without nippers from a sporting goods shop in Boston called "Stoddard's and I still have it on display.
At the time, I wasn't a fly fisherman however, I knew I HAD to have it because I knew it was a game changer. I attached
my Old Pal nippers to it, and IT to my Ideal vest and I never looked back despite going through more than a few versions & brands along the way.
I didn't fly fish so I seldom ran across well heeled fly fishermen on FFO water which may explain the ignorance, but almost everybody who saw it said, What's that thing hanging from your vest?"
All I know is I have never been without and never will be without zingers since those days...