For September silver salmon fishing in Yakutat I would recommend the Silver Salmon Fly Selection. It has a variety of great silver flies.
I would then add Dolly Llamas in #2 in Black/White, Pink/Purple, Pink/White and Tutti Fruiti. 2-4 each.
Finally, get a Rio Salmon Steelhead Leader 3-pack in 16lb test and a spool of Maxima Ultragreen Tippet in 15lb.
You will be all set!
Should be a great trip.