filling a fly box

nymphs pheasant tails,black stones, caddis, sucker spawns,glo bugs.there are alot more but there are some good starters.

Knochout,
 
Where are you fishing for trout (spring creeks, limestone, freestones)?  It will make a difference on nymph selection.  Learning about the different aquatic life will be your first step.  Then you can try matching nymph patterns to the critters you've located.
 
I'd add wolley bug for both trout and steely's.  I never go anywhere without Wolley bugs.

for trout;
i carry one box of strictly elk and deer hair caddis in different shades and sizes12-16. almost all streams in p.a. have some kind of caddis.
1 small box of nymphs; stones, pheasent tail, march browns, latex caddis and the like as previously mentioned
1 larger box for my buggers, thunder creek shiners and streamers that don't work yet
1 small box of small dries and small midges, #20-#18 include adams, b.w.o., blue duns and the like
 
from there it depends on the month.
1 box of drk. dry flies in the early spring
light shades of dry flies when it gets warmer
i keep my emerges in it's own seperate box,
 
i suugest don't mix nymphs with dries with big and small fies. as they accumulate and you'll start adding flies and forget which box hold what flies. so make it easy on yourself and get in the practice of seperating them in thier own box.
 
i also keep an extra box handy, if i strictly go out and don't want the weight and use my fanny pack i just put the flies i need in 1 or 2 boxes.
 

Hares Ear Nymphs, Pheasant Tails, Scuds, Sowbugs, Stone Flies, Blue Wing Olives, Caddis Larvae, Midges, Caddis Dries and a big one that everyone neglects.... crane fly larvae!