Wow, JZ. You're a fishin' fool. Sounds like a great trip.
Some Coho (Silver) Salmon fly patterns that seem to come up a lot for Alaska fish include Bead Head Canadian Leech (rust and black), Egg Sucking Leeches (especially purple and black), Tinsel Flash Flies, Polar Shrimp, Orange Comets, Popsicles and Bunny Flies.
There's also an article on the Kenai in the Great Rivers section of FAOL to check out too if you haven't already.
Here's a link that also may be helpful listing flies for steelhead and different salmon species including coho:
If you look at the left hand side you'll see "Fly Patterns". Roll over it to get more options and click on the "Pacific Salmon" link to get thumbnail pictures and recipes for the flies. Be sure to check the fly archives on FAOL too.
Here's a few other sites:
http://www.alaskaflyfishingonline.com/a ... index.html
Good luck, looking forward to pics of you with the silvers, and I haven't forgotten about the pics of that 5 foot pike you owe all of us when you catch him in Jasper.