I'd go with a mix of flies for different situations (water types), and a range of colors and sizes to imitate a bunch of different things:
Adams Parachute- 14, 16, 18 a good generic imitation for medium and dark mayflies, and a good pattern for slow water.
Light Cahill Sparkle Dun 16 and 18 a good imitation for light bodied mayflies (Cahills, Sulfurs) and a great in slower water. Because of the way it's constructed, and floats in the surface film, it also does triple duty as an emerger, dun and spinner (sort of).
Elk Hair Caddis tan body, tan wing 16, and dark olive gray body, dark gray wing 14. will imitate a lot of different caddis hatches. A good searching pattern in all water types too.
Ausable Wulff (or Royal Wulff) 14 and 16. A good fast water pattern- floats like a cork and is visible. My preference here would be for the Ausable Wulff since it's a bit more imitative of some of the larger mayflies (March Brown Gray Fox etc that you may run into). But both are great patterns, and good for searching fast water and a great choice for mountain streams and wild brook trout.
Griffiths Gnat- 20 to imitate small stuff which can very be frustrating. It's a good go to fly and you can often get some takes on a 20 Griffiths Gnat when the fish are actually feeding on much smaller naturals for some reason.
Yellow (or Orange ) Stimulator size 12- this imitates the yellow stoneflies that you'll get in the mountains. It also does a good job for large caddis/hoppers. It is a good floater in fast water, you can skitter it in slow water, and it is also a good fly to use as an indicator for hanging bead head nymphs under by tying a short piece of tippet to the bend of the Stimi.
I think I cheated and listed 6.... I better stop now....
These would be a good bunch to start with and build on--- pretty much for anywhere in the East or West, but including your NC and VA mountain streams. A local fly shop could also suggest specific flies based on conditions/hatches/water/and season, but these would cover a lot of bases throughout the year. You may also want to get a hatch chart for your local streams to get specific patterns from your local shop (or google), but generally for small mountain streams and brook trout they'll whack just about anything and don't tend to be very picky.
In other situations where trout are more selective, if you see fish eating naturals coming off the stream, try and match the size first regardless of pattern, then profile (upright wings for mayflies, down wings for caddis), then shade (light or dark). Even if it's not an exact match, you should have a lot of bases covered to get you pretty close.
Good luck!
mark
