For sockeye in Yakutat and similar areas, you'll be fishing for them using a high stick nymphing technique. A floating line with a 9' salmon/steelhead leader in 10-12 lb will be key. Most guys do not use indicators and go by feel. We suggest using size BB split shot set about 18" above the fly to get it down. BB is a good size because you can always add or subtract to find the right depth.
We have a large selection of flies. Sockeye flies tend to be smaller than other salmon patterns and can be very flashy to dull. Greens, Chartreuses, Reds and Oranges are often the go to colors, but pink, purple and naturals can be good too. Check out Sockeye Lightnings, Sockeye Lanterns, Montana Brassies and Copper Swans. The Sockeye Orange and Sockeye Green are really good if you're looking for a larger hook.
When fishing, look for fish that are pooled up and holding. These fish are a lot more apt to take a fly than fishing that are on the move. Some rivers and streams allow two flies. Think about fishing a tandem fly set up with the two flies of different colors set about 18" apart.
Best of luck!