Ard, You don't need to slim down. You look pretty good already.
I used to carry several of the half zillion flies I tied, and bags of knotted leaders. Most of the time, I only use 2-3 different flies, so I stopped tying everything under the sun. Once that was over, I started to carry fewer flies, but felt a little naked for a while. I've cited Lefty Kreh's article about flies from a few years ago before, and he says that for trout he carries para Adams and para Cahills (covers light and dark drys), GRHE and pheasant tail nymphs, Muddler Minnows, and Woolly Buggers. He says that he can catch trout anywhere in the world with just those flies, and would pick the Woolly Bugger if he were only allowed one pattern.
My vest includes a few extra leaders now, spools of 4X-6X tippet, nippers and hemostats, and some floatant. I have a little pocket that wet (wet with water) flies get tossed into, and since I usually forget to take them out, I just reach in there when starting a new fishing day. That means that I often never touch the couple of fly boxes I carry.
"what's the least number of flies you have or would take fishing"
Well I have taken ZERO flies on at least two outings, of course there was much cussing and such all the way back to the house after finding them on the dinning room table where i had left them.
LOL. Been there, done that. More times than I care to remember. Now I leave a box of flies in the glove box at all times, so at least I've got something.
We seldom get really warm but almost every year you can run into high 70's and bright sun that will be on you at 9 Am till 10 PM so it can get warm. The very next morning you wake up and it is only 48* and it begins to rain before you break camp. There is nothing you can count on but when the sun actually shines we soak it in because there aren't a whole lot of opportunities to do so. What you don't do is 'wet wade' the river in the picture is fed by a glacier and it never gets warm. It really isn't a small river I fish the same areas every year and know where the gravel bars are at, in the picture I was almost all the way across from where we parked the boat. Jeans and socks under those old LL Bean Wicked Tough waders, Commando
years ago when I lived in Invercargill and fish the Maturua, Oreiti, and Apramia rivers, (sometimes a few from the catlands for a treat) I use too have 6 flies, small dads favorites (#16/18) brown mayflys most are in NZ which is why most of what I tie is brown for mayflies, greenwells glory wet flies, coch y bondhy nymphs (its realy a wet fly with a tail) and drys, I had an adams but it never got fished, White bait streamers similar to the grey ghost, and peverile o'the peak.
This was when I had too pay $3 per fly, and didnt tie my own, now I have more than I could ever hope to fish and yet I keep tying them
as for leaving flies behind I have trouble remembering to birng boxes I have taken out to restock
Even forgot my rod once in such a hurry before my wife changed her mind with an off the cuff you should go fishing
I gave up on fly boxes while wading years ago, after losing about by 5th box of flies, that last time to an outgoiing tide instead of some river.
When wading, I now carry a half dozen flies in my shirt pocket; smokes, lighter, reading glasses and paper towels inside my hat. A small spool of tippet and clippers in my pants pocket, and a hat light clipped to my hat brim.