I was in Washington last year, and will be again this spring. This is my kit list :
Gear :
13ft 9wt Spey Rod- 650gr Skagit head
10ft medium floating MOW tip
10ft medium floating/sinking MOW tip
10ft T-8 sinking tip
10ft T-11 sinking tip
12ft T-18 sinking tip
11ft3' 7wt Switch Rod - 400gr Skagit head
10ft light floating MOW tip
10ft light floating/sinking MOW tip
8lb,10lb & 13lb mono/flouro
flies - for high water - pink, blurple, black, blue, orange - popsicles, intruders, skykomish sunrises, leeches, egg sucking leeches, MOAL leeches big prawn patterns. Hoh Bo speys, Dirty Hohs etc etc in 2/0 and above, flies 5-7"
for mid/normal water - the above in smaller sizes plus monkeys, green butt skunks, highlanders, buggers etc in #2 and above
for low water - traditional speys, skinny hohs, trout wets, General Practitioners, Ally's Shrimp, Ally's Cascades, etc etc in # 2, 4, 6 etc
if you want or need to nymph between runs or the water is very low. the guide will likely provide the latest 'hot' nymph.
the above is the standard go to's - but there are plenty of guides and steelhead bums who just fish blue/black or pink intruder or leech like patterns - on the basic idea that wild steelhead are dumb and will grab anything - but finding them and getting a properly swung fly in front of them is the real trick.
In 4 days on the hoh, queets, Sol Duc and Quinault rivers, my guide and other fishers were in the above camp - and put as much flash and UV material in their flies as possible in high glacial water.
best o luck.
cheers
Mark.