No you don't, and anyone with 500,000 flies will tell you the same
I do not carry so many flies with me at any point, but I do keep 1-2 extra boxes in the truck in case I fall in and lose my main box. The main box I carry is just a small, flambeau foam box with magnetic closure. I hate the ones with slots -- just a personal preference. They sit in my drawer collecting dust.
For trout, I mostly carry a variety of soft hackles with and without tungten beads, #14-16 CDC and elk dries in various shades, a few hackle spinners, and some Al's tricos in #22-24 and Al's rats in #22-24. Oh, and just a few green weenies as the only nymph I carry. Also, I keep just a few foam terrestrials...though there's not much I get with beetles/ants that I don't pick up with my darker EHC dries. So I could do without those honestly.
My flies feature a lot of soft hackle fibers and/or CDC fibers
. Those are my choice materials -- I subscribe to the "impression of life" philosophy vs. the matching every damn thing under the sun philosophy.
I rarely fish nymphs or streamers for trout. Just a personal preference, though I'm not against the idea -- I just kind of learned that I never do it where i trout fish and they go untouched...so why bother? Well, okay - honestly I hate dragging nymphs on the bottom and knocking off algae all day -- I think it sucks and it ruins the fun for me. However, I do fish dry dropper rigs pretty regularly. That's my "nymphing".
My wife nymphs like a woman possessed, and carries tungsten putty and many, many WD-40 nymphs in sizes #22-14.
Oddly, I fish almost nothing but
small streamers for warm water species in my backyard.