I have really worked to simplify my flies I fish with. Although I still tie 5 times as many kinds as I actually fish, I think I can get by with 2 (kinds for the day) and usually keep one on all day. In reality I probably only fish with 4 or so patterns all year.
1.) first choice - some type of topwater such as a Neversink/EHC or foam hopper. I pick one of these for the day and put 6-8 in an easily accessible box (clipped to outside of pack). May take the other kind but bury them down in another box down in the pack.
2.) then a nymph/streamer such as a WB or WW (sometimes a killer bug but using less and less).
Both in size 12 for trout, both in size 4 for warm water. I will change it up if fish are coming up to fly but not trying to take it, but I have got pretty confident in covering more water (not making 10 casts to every hole) as a better solution than changing flies as often.