For trout, I'm pretty much a fan of soft hackle style ties, midges, nymphs,classic wets, Muddlers and woolly buggers and woolly worms. For dries typical, March Brown, BWO, elk hair caddis and some of the royal style ties. So my materials reflect all that. For trout I would not be without grizzly hackle in cock neck and hen, natural hen as well or ruffed grouse second. In my box pretty much has always been those items, peacock herl, chenille, some gold beads, thin wire medium and small tinsel, rabbit dubbing in black, tan, mole grey, olive. Tan, black, red, olive and white thread, in 6/0 and 8/0 and 70 D. Floss in jade green, gold/yellow, burnt orange/reds. Elk hair, deer hair, mallard flank, calves tails in yellow and in white, squirrel tail in grey and in red or so called fox squirrel.. Turkey stuff, a couple of matched mottled feathers, biots in mahogany, black and olive. Bucktail or synthetics in white, brown , black purple and pink, orange and red. Antron yarn and poly yarns.
If you want to get started, I suggest getting materials for the flies you want to tie. The stuff listed above will automatically fill your box as you spread out your fly selection, LOL. Start simple, maybe woolly buggers or woolly worms. Just for the record, when I was first learning I started right there buggers and woolly worms, then to wet flies and streamers. I very quickly learned that I really needed a decent grizzly hackle neck, you can buy half capes or half necks to keep the cost down in the beginning.. For buggers you can get bugger packs or strung saddle . Ultimately, over the long haul of purchasing materials you will find your own favorites , in terms of hackle though there are some standards, which I listed in my first post.
Because I fish Maine, where both Brook trout and salmon are prevalent, I also stock some specifics to tie some of the standard patterns of that region. Caddis pupa of course can get both, Muddlers could but brookies really like them and extra really like them tied a certain way.. And classic and marabou Grey Ghosts are pretty standard streamers up there. Small Hornbergs are a good staple in New England, I don't know about your area. So again my box reflects that as well. Understand that "Rome wasn't built in a day", my box absolutely did not fill itself even in the first year of tying and traveling etc. In fact it's taken years/decades. And now materials offerings are changing and luring fishermen and tyers in, to some degree even myself. But classic materials still catch fish too.