"Picking your favorite gadget" is a really tough choice, but a fun topic!
OBVIOUSLY, as seen in my avatar, one of my personal favorites are my "Flip-Focals", just so I can see what breed of fish I've landed, on any given outing......
My Folstaf, also must be on my list, as it's saved me from numerous dunkings many times, when that "2 foot deep hole", was actually "deeper than my Folstaf's length"!
However, I have a newer, quite useful, "favorite gadget" in a little light I ran across not long ago while in a Walgreen's store..................
It's a small,"'flex light", that I'll never leave home without it, again!! About the same diameter as a "fat ballpoint pen"..........it holds 3ea. button batteries-(small, size G13s), has a ballpoint pen type clip and a 5inch long "flex neck" with a single LED bulb at the end. This light is unobtrusive, clipping nicely into the corner of an upper vest pocket, out of the way.
When I need light, (like, when it's dusk and I've landed yet another "monster" and I want to see what species it is, under the magnification of my Flipfocals), I simply twist the flex arm to where I need it, push the little rubber covered switch to turn the light on and I have about a 3-foot circle of light!
With the flex arm/head, it's great for searching in fly boxes, tying on #22 tricos and when walking back to the truck, in the dark, it throws a nice white circle of light ahead of me, when walking the trail! (which, unlike the one I had clipped to my hat........... I don't have to always be looking down to see the trail and when someone asks me something and I look up at them, in the dark, I don't blind THEM with my "hat light"..... by shining it in their eyes while talking to them!)
I've had it about, a year, it's on it's original set of 3 batteries and even being "dunked" a few times............it still works fine! Walgreen's price, for this light, (I've since, seen them many other placed as well), was "Two for $5.00". Money very well spent and my fishing buddy got the extra one, for free! But, I'm nice that way what can I say?