Um聟a little late in the game to be thinking about what to pack for a big trip like that, eh, Chris? But we聮ll see what we can do.
Mountain Hardwear Monkey Man Jacket

Weather-wise, you can expect lows around freezing, highs in the 60s, and a chance of rain. Although it will be chillier in the surrounding hills. But overall it sounds quite a bit like my fair city, Port Townsend, WA, more or less right now.
So here聮s what I聮d pack:
A light base layer. Ideal would be wool (Icebreaker Bodyfit 150, $50 each for tights and long-sleeve crewneck shirt; icebreaker.com). But a good synthetic is fine too, such as REI聮s Lightweight MTS (rei.com) is fine and costs about half of what wool does.
A midweight fleece jacket, such as Mountain Hardwear聮s Monkey Man Jacket ($140; mountainhardwear.com).
A warmer layer for your legs, something such as the Midweight version of MTS ($30).
Rainwear, such as the Marmot Oracle Jacket ($160; marmot.com) and Marmot Precip Pants ($90).
I聮d be inclined to also take one light insulation piece, maybe Mont-Bell聮s UL Down Inner Jacket ($140; montbell.com).
And of course you聮ll want general trekking gear, such as Ex Officio聮s Amphi Pants ($70; exofficio.com) and Air Stripe Light Shirt ($70). And accessories such as light gloves and a light fleece hat, that kind of stuff.
Are you part of a group? If so, they聮ll surely have water-filtering gear. If not, it聮s true that Potable Aqua iodine tablets ($6.50; potableaqua.com) kill baddies. But you also want to clean the water, so I suggest a filter and purifying solution. Pack an MSR SweetWater Microfilter ($70; msrgear.com) and SweetWater Purifier Solution ($10).
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